While at work I have to park outside and the light to get out of the parking lot sometimes takes several minutes. This means that I drive a short distance at low speed before having to sit at the light. On cooler days ( < 60 F) when I have to wait for the light my car will start idling rough after 1 - 2 minutes and when I take off the car doesn't accelerate smoothly. After I get up to speed then everything is OK. Also, if I don't have to wait long for the light then everything is OK.
I have tried twice to get the dealer to look into the problem, but they can't find anything. They kept the car overnight to see if it would do it after sitting out overnight, but still couldn't find anything.
Any thoughts on what it might be and how I can describe it such that the dealer can find and fix the problem?