whitefeathersnpr Posted March 21, 2013 Report Share Posted March 21, 2013 I have a 2005 Grand Prix GTP with about 98k miles on it. I have been having a couple issues with it. First when it is cold out (even after the car is up to temp) the rpms going down the highway are higher than they should be. I set the cruise at 72 and normally the rpm would be about 2200 then it went to about 2400 and now its at about 2500 - 2600. It feels like the engine is having to work a lot harder to maintain speed. This only happens when it is cold out, things are fine when it is warmer out but it is almost always an issue after a cold night. Next, after riding for a while with the higher rpms, the cruise control will randomly kick off. Sometimes it can be reset right away, sometimes I have to wait a mile. The latest development is that after driving the car, and having the rpm issues the car idles very rough in park (not noticable when stopped in drive), the rpms will jump from arou 900 down to 500 and even inbetween the idle is rough enough to feel the engine shutter. I only notice this if I have had issues with the rmps.I thought it might be the gas, but I ran the tank low and refilled it a couple times at different places (always with premium). I had the rpm/cruise issue last winter and thought it might be the coolant temp sensor, but the mechanic hooked it to the computer and said that is working fine. I have done the following: New plugs New wires New coils New MAF New brake pedal position sensor New brakes Oil changed regularly Changed super charger oil Radiator flush I am looking for any suggestions here. Thanks J. Quote Link to comment Share on other sites More sharing options...
Night Fury Posted March 21, 2013 Report Share Posted March 21, 2013 The RPM on the highway sounds like a transmission issue. You might check your fluid and watch the trans fluid temp. Shouldn't be getting much over 200. A slipping trans can indeed trip off your cruise control. Not sure on the rough idle. Quote Link to comment Share on other sites More sharing options...
whitefeathersnpr Posted March 21, 2013 Author Report Share Posted March 21, 2013 I have checked the fluid. The trans if full, the color and smell of the trans fluid are right. Trans temp doesn't get too hot, I don't know I have seen it get over 200. I would also think trans temp would be more of an issue during the summer than the winter. Thanks for the input. J. Quote Link to comment Share on other sites More sharing options...
95 vert Posted March 21, 2013 Report Share Posted March 21, 2013 Sounds like maybe the torque converter isn't locking up? Idle issue may be the electronic throttle body/possible vacuum leak and it's possible this could be the lockup issue. If the throttle position sensor isn't reading correctly, the idle will fluctuate and converter lockup may not work. Hope this helps. Quote Link to comment Share on other sites More sharing options...
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