My daughter has a 2003 Grand Prix GT. She has been having some problems where the engine will race up and down on it's own, as she drives. Sometimes it acts as though the cruise control is on. At first she thought it was a transmission problem. We were going to take it to a transmission repairman, but after I drove it, I thought it acted the same as one of my cars when the Idle Air Control Valve went bad. Replacing that fixed the problem on my car. I replaced that on the Grand Prix and performed a good cleaning of the Throttle Body. It helped, but it has now been several weeks since this was done and she claims it is still acting up. She also said it acts worse in the afternoon after the outside air has heated up, and really acts up (lurching and jerking and high reving at stop lights, etc.) when she runs the AC. I have not driven it since she brought it to me yesterday to look at it. So today I will drive it again and try to see how it is acting and figure out what it might be. My next thought is the Mass Airflow Sensor may be bad, but I am not getting a check engine light or a code, so I really don't know. Also, could it be the throttle position sensor? Any help would be appreciated.
