Having an issue with a 2000 Grand Prix GT. When the car is cold, it runs great with no issues. After it is driven for around 30-45 minutes it starts to get a surge when you let off the throttle. During the first part of driving it, when you let off the throttle from 50+ mph the rpm will drop to ~1500 while coasting, and then drop down as you apply the brakes to stop and come to rest ~800 at a stop. After the engine is hot, when you let off the throttle, it will drop to around ~1500, then suddenly drop to below a 1000, then surge quickly back up to 1500. It will do this 4-5 times every time and then stop when you get below ~25 mph. Even while applying the brakes you can see and feel the surge. I did the TCC check by pressing the brake while it was engaged and it releases and re-engages with no problems. It also does this if I slide into neutral while coasting and slowing down, of course you can't feel the surge in neutral but you can hear it and the rpm gauge jumps from ~1000 to 1500. The only codes they pulled were for the oxygen sensor which was replaced. Otherwise the car runs great. Anybody had anything similar?
