I have just recently had the same problem.
The GM mechanic changed my thermostat as well as flushed the radiator, after doing all that and $550.00 later, the car still runs hot and was overheating even while driving. I took my vehicle to a friend of mine who works at NTB, and they found that the main cooling fan was not coming on at all. Also per the GM Mechanics my friend tested the heads because the GM guys said I had a leaking head casket, and friend found nothing wrong with the heads. So he replaced the fan and relay switch (and whatever else he needed to do) and again after all that and another $550.00, the car will drive fine and not over heat until you stop and the car will idle low somewhere around 500 rmp and again will over heat. They have had the car for 3 days trying to figure out what is wrong. The only thing I can find online is that the throttle body is not working properly and will cause the car to idle rough, however I can't seem to find anything about the over heating.
I am looking for some ideas as to what could be the problem. And also if I find anything out I will post.
Sunday, February 17th, 2013 AT 7:21 PM