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1985 380SL idle high when hot

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Re: 1985 380SL idle high when hot

It's probably either the idle control unit or the idle control valve. I forget if it's in a different place on the SLs or not, but on the SE the idle control unit is between the 2 firewalls - will have part number 002 545 33 32 on it. The idle control valve is the silver cylinder at the front of the air cleaner just below the air cleaner.

Once you find this idle control unit, if you find that by opening the case and flexing the board you can restore the idle to the proper speed, you have found your problem.

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Re: 1985 380SL idle high when hot

Marlinspike,

Not sure what you mean "between the 2 firewalls"? Anybody out there got the specific location for a 380SL

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Re: 1985 380SL idle high when hot

Look behind the glove box. You'll need to remove the glove box liner for access.

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Re: 1985 380SL idle high when hot

That sounds right, behind the glovebox.

This picture is from a W126, but it's the same part, just in a different location, so it should give you an idea of what you're looking for.

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Re: 1985 380SL idle high when hot

85 380 With a similiar problem. Except when hot idle would go to low and stall. I was told idle control unit or idle control unit. It turned out to be the ignition control unit. Located on driver side fender well.

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Re: 1985 380SL idle high when hot

Idle going to 1600rpm is because the idle control valve is going to open mode (i.e. cold running mode), either because it itself is broken or because the idle control unit is telling the wrong message (it could also be a vacuum leak, but that wouldn't be my first suspect)

Shutting off when hot I would never think to be the idle control unit or valve, but rather would think the ignition control module because when they go bad they tend to stop functioning when hot. I hope it wasn't here that someone told you the idle control unit/valve, and if it was I hope it wasn't me as if I did it would only be because of misreading.

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Re: 1985 380SL idle high when hot

I am the original poster and it seems to have cured itself. No recurrence of the issue over the last few days.

The car had not been driven much over the last few months. Once I got it out and ran it some it seems to be working fine. Not a single instance of it reverting to the high idle when hot. It sounds great at idle and accelarates well. Gas milage appears to be good but I won't know for sure until I get it out for a long run.

I am guessing (and its only guessing mind you) that the idle control valve may have been mis-behaving a little since it had not been driven much and now that I've had it on the road regularly it has settled down. Can't think of anything else.

Now all I have to do is get the ventilation blower working and replace the A/C components and I'll be fully functional.

Thanks for all the help from this forum - it is a real help.

Dan

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Re: 1985 380SL idle high when hot

I am the original poster

Well- It started doing it again so I guess it was not just a matter running it some. Guess I am back to the drawing board, but with the info I have gotten I am sure I can figure it out. I found the Idle Speed Controller under the glove box. It was actually hanging down and "fell out" It is still electrically connected but I would imagine that the PO must have put in a new one at some time or another since it wasn't attached up under the dash behind the glovebox. Just a guess. That would seem to mean that the culprit is most likely the idle speed valve. When I get back from a trip I'll scope it out.

Thanks again

Dan

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Re: 1985 380SL idle high when hot

I would wager it's the idle control unit, not the valve, given that it stopped and came back. I bet if you whack it with a lug wrench when it's doing high idle it'll go back down. Try popping the case open and flexing the green board, I bet you'll find that you can get the idle to go down with the proper twist.

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Re: 1985 380SL idle high when hot

Thanks Marlinspike,

I am away from home but as soon as I get back I'll give that a try. By the way, with a name like "marlinspike" I have to believe you have some connection with the sea or sailing? :D

Dan

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Re: 1985 380SL idle high when hot

I did some sailing in college, but it's actually a Tintin comics reference.

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OT: Re: 1985 380SL idle high when hot

marlinspike;174216 wrote:
but it's actually a Tintin comics reference.

Blistering barnacles! The Captain would be proud. :)

Did you read Asterix and others like Lucky Luke as well?

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Re: OT: Re: 1985 380SL idle high when hot

MCama;174219 wrote:
Blistering barnacles! The Captain would be proud. :)

Did you read Asterix and others like Lucky Luke as well?

Asterix, yes, but no to any others.

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Re: 1985 380SL idle high when hot

Billbill;173882 wrote:
85 380 With a similiar problem. Except when hot idle would go to low and stall. I was told idle control unit or idle control unit. It turned out to be the ignition control unit. Located on driver side fender well.

I've got the same problem with my '79 450SLC, Will it be in the same location?

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Re: 1985 380SL idle high when hot

Sorry to bring back an old thread but I just recently gotten a hold of the old family 1983 350SL. Seems to idle around 1600 while in Park, but in Drive idles much lower. Idle control unit problem?

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Re: 1985 380SL idle high when hot

mb380sldms;174022 wrote:
I am the original poster

Well- It started doing it again so I guess it was not just a matter running it some. Guess I am back to the drawing board, but with the info I have gotten I am sure I can figure it out. I found the Idle Speed Controller under the glove box. It was actually hanging down and "fell out" It is still electrically connected but I would imagine that the PO must have put in a new one at some time or another since it wasn't attached up under the dash behind the glovebox. Just a guess. That would seem to mean that the culprit is most likely the idle speed valve. When I get back from a trip I'll scope it out.

Thanks again

Dan

I had the same problem with my 85 380SL. Solved it when I found a vacuum line disconnected. It was on the left side of the air cleaner.

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Re: 1985 380SL idle high when hot

I am the original poster and I think I have figured it out.

This morning it was cold here, about 15 degrees C (relatively - eat your heart out Wisconson). The car started right up but would not come off of high idle when I started to drive it. Performance was nill - whenever I hit the accel it just did not respond and almost died. I tried tapping and flexing the idle control box (in side the passenger side behind the glove box - no change - still idling at about 1400 or so. :confused:

Then I opened the hood and tapped lightly on the cold start valve (I think that is what it is called) on the top of the engine just in front and partly below the air cleaner. Bingo - the idle returned to normal for a warmed up car and it drove great. :D

So - I surmise that the cold start valve is sticking. Is it possible to take this part off and somehow clean or refurbish it and what is the procedure for that? If not then I guess I'll have to either keep a "tapper" in the car or get a new part.

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mb380sldms

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Re: 1985 380SL idle high when hot

Taking it apart is a big pain. Cleaning it is easier. Take it out of the car (just undo the hose clamps and it comes out) and flush it out with lots of brake cleaner. Be sure to do this outdoors...probably even better to do it outdoors using a product like Wurth Brake Cleaner which is much less hazardous than other brake cleaners).

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Re: 1985 380SL idle high when hot

marlinspike;180638 wrote:
Taking it apart is a big pain. Cleaning it is easier. Take it out of the car (just undo the hose clamps and it comes out) and flush it out with lots of brake cleaner. Be sure to do this outdoors...probably even better to do it outdoors using a product like Wurth Brake Cleaner which is much less hazardous than other brake cleaners).

Tried the brake cleaner and now it always is on high idle. Will not come off high idle at any time not matter what I do and no matter how hot the engine is or how long it runs!

It also seems like the vacuum is not as good as it used to be. Before when I ran at a steady speed it was always on or nearly on the peg in the black and even when I accelerated (slowly) it went midrange on the vacuum gauge. It only went high in the red when I accelerated pretty hard. Now it goes into the red with only a little accelerator and has no "varoom" at all. Guess I did something to the cold idle valve when I tried to clean it? Maybe I accidentally disconnected a vacuum line somewhere. I'll check that tomorrow morning.

Guess this pretty much pinpoints it to that valve though since it is the only thing I messed with and not it is always on high idle. Did I need to lubricate the valve a little after I cleaned it? Is there a way to "exercise it" with it off the car?

Marlinspike - don't worry about the advice - I was desperate for some ideas so if it didn't work it still pinned it down to that part so I can at least replace it if I can't get it working/

Smokey73

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Re: 1985 380SL idle high when hot

mb380sldms;181130 wrote:
Tried the brake cleaner and now it always is on high idle. Will not come off high idle at any time not matter what I do and no matter how hot the engine is or how long it runs!

It also seems like the vacuum is not as good as it used to be. Before when I ran at a steady speed it was always on or nearly on the peg in the black and even when I accelerated (slowly) it went midrange on the vacuum gauge. It only went high in the red when I accelerated pretty hard. Now it goes into the red with only a little accelerator and has no "varoom" at all. Guess I did something to the cold idle valve when I tried to clean it? Maybe I accidentally disconnected a vacuum line somewhere. I'll check that tomorrow morning.

Guess this pretty much pinpoints it to that valve though since it is the only thing I messed with and not it is always on high idle. Did I need to lubricate the valve a little after I cleaned it? Is there a way to "exercise it" with it off the car?

Marlinspike - don't worry about the advice - I was desperate for some ideas so if it didn't work it still pinned it down to that part so I can at least replace it if I can't get it working/

Smokey73

I don't think cleaning has damaged it. I've soaked on in a tub of brake cleaner for an hour before, no harm resulted. It may just have been on its last legs.

Shouldn't have any need to lubricate it. I'm thinking a line got disconnected around there. Where is the economy gauge with your foot on the brake, car in D, at idle (you'll have to do this before the idle goes high for the reading to be meaningful).

On a warm engine when it's high idling, take a volt meter to the plug that goes to the idle control valve. It should read ~12V. A way to test the idle control valve is to apply 12V to it. You should hear it click closed.

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Re: 1985 380SL idle high when hot

Me thinks your overload protection relay is defective.

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Re: 1985 380SL idle high when hot

marlinspike,

I'll give a shot at checking the voltage at the connector and trying to hit 12 volts at the valve to see if it clicks.

I can't get it to idle anything but at 1500 no matter how hot it is so I can't check the vacuum there. Previously it was on the black pag at idle with the foot on the brake.

Thanks for the troubleshooting tips.

Smokey73

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Re: 1985 380SL idle high when hot

pch2021;181151 wrote:
Me thinks your overload protection relay is defective.

I'll bite - what and where is the overload protection relay? How do I find it and how do I check it?

Thanks

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Re: 1985 380SL idle high when hot

pch2021;181151 wrote:
Me thinks your overload protection relay is defective.

If that were the case, wouldn't his ABS light be on?

The idle isn't 1500rpm when the engine is cold is it?

I have a "spare" idle control valve. I say "spare" because I will need it back at some point. Also, it has been modified, so you wouldn't want to leave it in your car, but it does function (so you'd be able to see if that is in fact your problem).

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Re: 1985 380SL idle high when hot

Go to the url below;

http://www.mesaperformance.com/faqs/idle.html

these are the best directions I have seen for troubleshooting the Idle Control Circuit. Even though it's written towards the BMW the only real difference is the screw for adjustment. I have used this procedure on my 533i and was able to stabilize a hunting idle by using the "kludge" until I got a new ICV.

The 380SL I have now actually had an ICV from a BMW with the screw and it works but I changed it to the MB version just to try and get this car more to stock condition.

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Re: 1985 380SL idle high when hot

Marlinspike and all

Well I checked the voltage at the connector when hot and it read about 1.4 volts. I then put 12 volts on the Cold Idle Valve and it worked perfectly and the idle went down to normal. So that leads me to believe that it is in the Idle Control Unit, not the valve. Not sure why I got 1.4 volts and not 12. Seems like it would be all or nothing? So the valve is good and I'll have to look elsewhere for the problem.

I'll look at tht link for troubleshooting the ICU and see what that yields.
Thanks again.

Dan

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Re: 1985 380SL idle high when hot

romank;181162 wrote:
Go to the url below;

http://www.mesaperformance.com/faqs/idle.html

these are the best directions I have seen for troubleshooting the Idle Control Circuit. Even though it's written towards the BMW the only real difference is the screw for adjustment. I have used this procedure on my 533i and was able to stabilize a hunting idle by using the "kludge" until I got a new ICV.

The 380SL I have now actually had an ICV from a BMW with the screw and it works but I changed it to the MB version just to try and get this car more to stock condition.

Could you explain to me what the kludge does? Do you know what the part number is? From reading that website, it seems like this is something I have a use for.

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Re: 1985 380SL idle high when hot

mb380sldms;181165 wrote:
Marlinspike and all

Well I checked the voltage at the connector when hot and it read about 1.4 volts. I then put 12 volts on the Cold Idle Valve and it worked perfectly and the idle went down to normal. So that leads me to believe that it is in the Idle Control Unit, not the valve. Not sure why I got 1.4 volts and not 12. Seems like it would be all or nothing? So the valve is good and I'll have to look elsewhere for the problem.

I'll look at tht link for troubleshooting the ICU and see what that yields.
Thanks again.

Dan

I was wrong about there should be 12V at the connection, but I was correct enough that I didn't bother correct it. IIRC there really should be like 9V (because it's turning the 12V on and off). So, clearly your valve is working and it's not being given enough voltage.

To me that says idle control unit. I hate to say it, but I recommend buying new (look in your latest Star - I remember there is a dealer advertising 25% off for MBCA members and another advertising wholesale prices). I went through 3 "working" idle control units from salvage yards. None worked. I thought my car was blowing them. Bought a new unit...works fine.

You can try touching up all the solder joints on the board, but I never got this to work for me.

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Re: 1985 380SL idle high when hot

It could also be one of the temperarture sensors.
I am just not sure which one it is.

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Re: 1985 380SL idle high when hot

Marlinspike,
the Kludge is a manual restriction of the airflow through the ICV. If the slide inside is not quite moving correctly then the idle hunts, mine was really bad up and down 500 - 700RPM. I used a steel washer and some duct tape to restrict the flow and it completely smoothed out to 700. I had to play with the washer size a little since it affected cold start too but it worked until I could get a new ICV and proved the ICV was bad. The complete directions are in that writeup from the url above.

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Re: 1985 380SL idle high when hot

romank;181176 wrote:
Marlinspike,
the Kludge is a manual restriction of the airflow through the ICV. If the slide inside is not quite moving correctly then the idle hunts, mine was really bad up and down 500 - 700RPM. I used a steel washer and some duct tape to restrict the flow and it completely smoothed out to 700. I had to play with the washer size a little since it affected cold start too but it worked until I could get a new ICV and proved the ICV was bad. The complete directions are in that writeup from the url above.

I guess my question is does it let it go higher than normal? I.e. is it like a mechanical adjustment that can be used to adjust the idle? I've got a non-stock car, I'd like a way to adjust the idle beyond just "the computer says it's right"

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Re: 1985 380SL idle high when hot

Nope that won't do it. It only stabilizes it.

What is "non-stock" about the car?

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Re: 1985 380SL idle high when hot

Marlinspike et al.

Yea, the valve seems to be fine. It either has to be the Idle Control Unit (ICU) or a sensor. Before I jump on buying a new ICU do you know which temperature sensor is used to tell the ICU that the temp is up or other sensors? I had a poor connection on the temperature gauge sensor on the very front of the water housing. I'm not sure that this is the one used for the ICU though. I fixed it with a new connection and it is sending temperature to the gauge fine.

Anyone out there have a known working ICU they are setting on that could loan it to me to check out if that is the problem? Maybe a spare or one that is on a car you are working on right now? I'd be happy to pay postage both ways and would be sure to get it back to you. I'd even write a check for the value and you could hold it until I get it back.

If it turns out to be the ICU I'll go with a new one.

Thanks for all the help everyone.

Dan

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Re: 1985 380SL idle high when hot

IIRC it uses a few different temp sensors, and I think even an oil pressure sensor. I have quite a few idle control units here that work when you flex the board just right, but none that work consistently, sorry.

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Re: 1985 380SL idle high when hot

Did you make sure your timing is correct? The idle control cannot adjust down if the timing is advanced too far.

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Re: 1985 380SL idle high when hot

Original poster here!
This is getting frustrating, but I bet that is not new for anyone on this forum. I give up

Last week it was working perfectly. I took it for a 160 mile drive from Beaufort SC to Jacksonville Fl with no problem. The idle was perfect when cold and hot. It ran fine and the vacuum was great. When idling while warm the vacuum was on or near the black peg. When you accelerated, if you did not stomp it it would keep good vacuum and be about half range. When running at 65 to 70 mph it was still fully in the black or just the edge of the where the red "wedge" starts on the gauge. Seems like that is about as good as you can expect for a car at 70 mph.

About two days later I start it up and it stays at 1500 rpm and won't come down to a normal idle no matter how warm it is. Marlinspike loaned me a couple ICUs that needed a twist to work but no matter how I twisted them, the RPM stayed at 1500 rpm.

Any ideas out there? I hate to just buy a new ICU and end up with the same problem. I know if I hit the idle control valve with 12 volts the idle drops immediately to about 600-700 rpm and is as smooth as silk. That tells me that the valve itself seems to be working so for some reason it is not getting the right signal. Is there a troubleshooting guide for the ICU that tells what all the appropriate signals are to the ICU so I can check the various inputs? Does anyone know specifically what temperature sensor tells the ICU the engine is warm and its time to send the signal to the idle control valve?

Any help would be appreciated.

Thanks

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Re: 1985 380SL idle high when hot

One thing I can think of (actually happened to me, don't know why I just now thought to mention it) is maybe the connections on the plug that plugs onto the ICU have worked loose. Pop the back off the plug, take a picture (so you know what wire goes where), then pull out each wire and close the connector end with a pair of needle nose pliers so that it goes on the ICU tight.

Weird that the twisting didn't work (the way to twist them is grab the top corners and twist in the direction that would be clockwise if viewed from above), that's why I'm thinking it's something other than the ICU. There are quite a few things that input to it, and it would be rather annoying to track them all down, so here's hoping it's those connectors.

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Re: 1985 380SL idle high when hot

Marlinspike,

I did get the boards and tried twisting about every which way but loose. No luck.

I'll try the connectors next. Odd that it worked for awhile. Now that I think of it I may try pulling the Over Voltage relay and check that again. When it worked I had checked the fuse (same one for the heater blower motor) and also pulled and looked at the relay the day before the trip. I'm just wondering if when I did that the relay made contact for awhile and worked for the trip but doesn't make good contact now. I don't have the ABS light though but I'm keeping my fingers crossed its some sort of contact issue. I'll keep plugging away and try those two units I got from you. I'll send them back in a few weeks after I've either figured it out or just come to the end of my rope. Thanks for your help.

Smokey73

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Re: 1985 380SL idle high when hot

No need to send those back, I have no use for them.

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Re: 1985 380SL idle high when hot

These attached diagrams might help you. There are only a few sensors / switches and you can easily check each one when it's running. The best would be when it is in that high idle state, you just disconnect a sensor and see if it goes away and if not just jumper the connector and see if it goes away. A thought here is the Lambda ( O2 sensor ) plays a big part in feedback on lean / rich conditions and then the system is supposed to react accordingly. Mostly the frequency valve will change it's duty cycle. If it's idling high you could just pull the connector off the frequency valve and see if the idle comes down.

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380idlecntrl2.pdf 362.54 KB
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Re: 1985 380SL idle high when hot

I've just hopped into the last page of this post, but I'm betting that you have an intermittant fault in the OVP relay causing the high idle.

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Re: 1985 380SL idle high when hot

I have been playing around with the new WIS/ASRA software today trying to learn how it works and I stumbled upon 2 reported issues of "idle speed temporarily > 1100 rpm at operating temperature" and " idle speed at operating temperature occasionally > 1100 rpm"

The culprit was the TPS out of adjustment or bad.

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Re: 1985 380SL idle high when hot

romank,

You wouldn't happen to have page 209 of the document you posted. It shows the location of the components. It would be helpful

Also what is the TPS? Since I don't know what that is I can't check it?:confused:

Thanks,

Smokey73

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Re: 1985 380SL idle high when hot

I'm glad you asked about that document. Somehow when I installed the service manual CD multiple documents were installed in other directories so when I tried to open them from the menu they were not found. This time I did a little more searching and found them so it helps me too Thumbs up

It's too big to attach ( 1Mb ) so if you PM me your email I can send it to you.

The TPS is the throttle position switch. It's attached to the throttle body and sends the signals to the ECU on idle or full throttle positions. You can just barely see it if look on the drivers side of the throttle body, it will have a wire that is attached that should come out to a large 3 pronged connector, some information is attached.

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Re: 1985 380SL idle high when hot

Interesting turn of events - helps me focus down on the problem.

Yesterday when I started and let it warm up, it ran perfectly and idled perfectly when hot, about 600 rpm and smooth as silk. I took that opportunity to try a few things.

Unplugged the ICU and it went to 1500 rpm right away, plugged it back in and down to 600. Took one of the loaned ICUs that I had (thanks) and plugged it in, still 1500 rpm but twisted it this time and just like advertised, it came back down to 600 rpm when I held it just right. I did not have to twist mine so I conclude that : My ICU is okay and the problem is elsewhere. Plugged my ICU back in and 600 rpm and smooth.

NEXT

Unplugged the OVP relay. Idle went immediately to 1500 rpm (note I did not get the ABS light as I expected) I plugged it back in and it went back to 600 rpm. It could still be an intermittent OVP relay failure but I am guessing it may be somewhere else, like one of the sensors that romank has identified. (Hope I can get page 209 soon).

Anyway I feel confident it is not the Idle Control Unit (ICU) and is not the Idle Control Valve so I can focus on the OVP and the sensors. I think it will be easier to check the sensors once I identify all of them from the files romank sent and can find them than to easter egg hunt by replacing the OVP and individual sensors.

Once it is warm and in the high idle conditions I can start troubleshooting again. I am assuming that most if not all of the sensors are "open" or "closed" type sensors and I can check them by either pulling them to see if that drops idle and if it doesnt by shorting across the wire and seeing if that cuts the idle. Are there any that I will damage if I do this? Help is appreciated.

I know there is a different procedure for troubleshooting the Throttle Position Sensor and romank has already provided that procedure.

I really appreciate everybody's help on this. I'll let everyone know what it is when I finally figure it out. The "nuclear submariner" doesn't like easter egg hunting.

Thanks again.
Smokey

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Re: 1985 380SL idle high when hot

Smokey, Where can i find the OVP relais? How does it look like?

Marion

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Re: 1985 380SL idle high when hot

Marion,

The OVP relay in a 1985 380SL is located in the kick panel of the passenger side - to the right where your right foot is. That panel access goes to the fuse box. You may have to take out a few screws though to remove the whole kick panel - the hole opened up when you pull the access panel for the fuse box is pretty small. The OVP is above and to the right of the fuse box itself and a little hard to reach. It is a small silver square relay with a fuse in the end of it. Check the fuse and the relay itself.

For those wanting an update - For some reason it works fine now, the idle perfect and I really didn't do anything but pull the Idle Control Unti and the OVP and plug them back in. Plus I have been driving the car more so I guess I just chalk it up to "magic" unless it fails again and I can start the troubleshooting again, but there no shooting to do if there is no trouble right now. Thanks for all the help.

Smokey

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Re: 1985 380SL idle high when hot

Smokey, clear explanation, found the relais. Thanks.

Marion

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1976 450SLC
Re: 1985 380SL idle high when hot

I was having the same issue...I'd start up the 450SLC and the idle would set itself at 1,2K - 1,4K rpms..

Turns out that the vacuum hose, behind the air cleaner, up against the fire wall on the top of the manifold was "loose" or cracked (cloth-covered hose)...it's the hose that feeds forward under the fuel distributor and towards the TB. I had a mechanic with longer arms than I'll ever have and skinnier fingers replace it...

Problem solved.

Now, I need to have a "complete" tune-up and tweek-in...with the engine both cold and warmed up...but at least, right now, she's idling around 650rpms... :Thumbs up:

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Re: 1985 380SL idle high when hot

Well, its back and just as unusual as ever.

It has been running at a high idle when hot lately so I tried a little troubleshooting (see other post on a oops!)

I started it and it went immediately to the high idle then at some point when it warmed to operating temperature it went down to normal idle. I then shut it off and immediately restarted it. It immediately went to high idle. My conclusion is that the problem is electrical not vacuum. It is unlikely that a vacuum leak would suddenly show up but more likely that the some electrical component is the culprit.

Later - the next day.

When I started the car it idled fine (cold start at about 80 degrees outside temp) I measured the voltage at the idle control valve and it read 13.5 volts. I found this odd since it was cold and had not reached operating temperature. Then later when it warmed up the voltage went to about 1.6 volts and the idle went to 1200 rpm or so - just the opposite of what I would expect.

I then tried to jumper across some elements to see if the idle came down. That is when I made a big "O No" and jumpered across the idle regulator connector (not at the idle regulator but at the wire supply side) The car immediately died and will not restart. I squirted a little starting fluid and it starts on the fluid but immediately dies as soon as the fluid is exhausted. Conclusion - I shorted out something in the fuel supply system.

Any help with the initial problem and the later one where I shorted out something would be appreciated.

Thanks in advance.

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Re: 1985 380SL idle high when hot

If you turn the key to the start position, do you hear the fuel pump whirr? I'm guessing not, which would mean you've blown the fuel pump relay I'd think. Not sure where it is in an SL, but it's in the fusebox in an SE, has the redline written on the side of it. If the fuel pump isn't whirring jump the sockets for pins 7 and 8 (NB: this is a testing measure only, you lose some safety features by doing this, like the mechanism to cut the fuel pump when the engine shuts off), I think it's terminals 30 and 87.

If you can tell me which wires you jumped when you had the oh no, I could probably tell you what you fried.

PM your email address and I'll send you the wiring diagram in pdf form (it's for an SE, but it should be pretty similar).

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Re: 1985 380SL idle high when hot

marlinspike - Thanks

I got around to getting to the fuel pump relay today and sure enough, there is a burned link. My son has a pretty steady hand and has offered to give it a shot.

Thanks again

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Re: 1985 380SL idle high when hot

Thanks all,

My son, who has a much steadier hand than me, repaired the burned link on the Fuel Pump Relay and not it starts find. I still have to figure out the high idel issue but at least it will start and run now. :smilie:

Smokey

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Re: 1985 380SL idle high when hot

How did you end up deciding that the high idle is not caused by the idle control unit? I figure that with the twisting action working on the ones I sent you, that'd be it. Next time it's idling high try taking one of the ones I sent you now that you know it works with twisting. Sometimes the boards will work fine until the board itself gets hot (I guess some small crack is expanding or something).

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Please note that all the

Please note that all the smileys in this were recommended by my sons who are watching me type this right now. They may not mean anything, but look like a lot of fun.

Marlinspike, I agree with your logic.

I wanted to report that I think I just encountered and solved this problem on my Mother-in-Law's 1985 380SL with about 70k miles.

Symptoms: high idle, starting around 1200 when cold, going to a steady 1500 when warmed up. Not intermittent at all.
This is my mother in law's car, so I never drive it myself.

Idle control valve is less than a year old.

After reading this complete thread and the links, I checked the OVP (fine), then removed the cover to the Idle Control Unit. With the engine idling at 1500, I spent several minutes bending the board, but finally found the right way to do it to make the idle drop to around 800. I then removed the board from the car and re-flowed every solder joint (like 200 of them) and re-installed. It now idles at 750, steady. I realize things may not work in the long run, and I may end up needing to buy a new one. But I wanted to give people another data point to judge by. The testing seemed to very clearly show the ICU as the problem. A lot of board bending was required. And re-soldering every joint seemed to do the trick, at least in the short term.

Thanks for the help on this.

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Thanks

I know this is an old thread, but it has really helped me out.  I just bought my first 380SL, a week after purchase I started to have a high idle issue.  This thread is the best one out of the 4,000 others I have read.  It deals with all the issues, and everything is finally making sense.  I'm going to clean my idle control valve tomorrow, and already ordered a new ICU as it seems like a common problem or will be in the future, and at the very least it will eliminate one variable from the equation.  THANKS!

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1984 380SL, Noels engine with 10k miles, chassis 150k.

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Help?!

So I've read over a lot of the threads, still having issues/questions.

I have an '84 380 SL.  When cold, it will idle properly.  After I drive for about 5 minutes, the high idle issues starts, goes up to about 1300-1400.

I looked at the fuses (haven't checked with multimeter though) and none of them are blown.

I thought I had an idle control unit issue.  I took apart the glovebox, took out the ICU, and found that it had been replaced by the previous owner in 2007/2008 (which I confirmed with him through a follow up email).  

I then took out the idle control valve, cleaned it with brake cleaner as suggested.  When installed and disconnected from ICU, idle was 1500.  When I reconnected it, idle briefly went down to 700ish, then 15 seconds later resumed normal high idle.  (During this process I discovered the wiring connecting to the ICV was corroding, so I rewired the connecting harness for a good connection).  I just installed a new ICV, and the idle issue is still there.

Any suggestions?  Is it possible the remanufactured ICU is faulty after just a few years?

I've looked at all the rubber/lines and they all seem to be good.  Is there a specific spot I should be looking at?  (btw, engine was replaced with remanufactured Noels approximately 10k miles ago in 2008, so I'm guessing all bad rubber was replaced then).

Thanks for any help in advance!

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High idle and no heat

I have the high idle problem and I have noticed that when it idles high I also have no heat. What would be teh common link here?

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