2003 Pontiac Sunfire • 180,000 miles

My 2003 pontiac Sunfire will excellerate unexpectedly while driving or at a stop while in park or netrual to 3000 to 4000 RPm causing the car to surge. It will also fall below 750 RPM while idling and stall at a stop as well. When the car is not doing this it works fine. The problems seem to happen when the car is warmed up and the engine coolant temp is at 90C on the temp guage. Temp guauge stays at normal consistant reading and does not fluctuate. I have changed out the IAC sensor and The Throttle Body Position sensor. I had a mechanic check for codes and there are none. I change the MAP ( Manafold Air Pressure sensor) and the Mass Air flow Sensor on the air intake assemble between the air filter and the Throttle Body. Car is still doing the same thing. These problems are occuring in the winter months with outside tempertures between +10 and -20C.
February 11, 2013.

Try cleaning the throttle plate on both sides first. With choke cleaner

Feb 11, 2013.
Did that and cleaned the AIC intake.

Feb 11, 2013.
I really dont know wht to tell you unless it's a vacuum leak of some sortor unless your mat on floorboard is getting stuck in throttle assy. Maybe due ot ice from temps outside. This doesn't have a K& n type air filter on it as they can cause jproblems to trnasmission as well as engien problems due to oil in them. Other htan that it may be a programming issue with pcm that is doing that. Can't think of anything else.

Feb 11, 2013.