Can anyone help? Idle problem

[warmhrt]

I have had problems with my car running rough and surging idle. When I started car today, idle was extremely high and wouldn't drop down while driving. It felt as if the car was driving itself. Only when i brake to a stop, car would drop idle, then stall. If i try to put in neutral while driving, it would rev even higher and stay there. After about a half an hour of driving around, I shut car off to go into store. When started car again, it idled normal with no problems? Its an 89 corsica, 2.8L, automatic. It's throwing same codes again of parts i have replaced.
This is what has already been done: PCV valve and hose under plenum replaced. New gaskets on plenum, throttle body, egr. Replaced oxygen sensor, map sensor, IAC valve, because i was getting codes 33, 35, 44. I have tried cking for vacuum leaks but don't know if i am missing any. How can i find what it is to fix it? Can't afford to keep replacing parts..poor. Please help.

[SappySE107]

Check your grounds. You really need to put it on a scanner and see what its doing. It could be a bad wire in the harness or at the plug. Pull the IAC out and have someone turn the car on. Hold your thumb over the pintle on the IAC so that it doesn't fly off. Turn the car off and see what the IAC does. It should push out and then pull back in some. If not, that is your idle problem. If your coolant temp sensor is off it will cause problems with idle but im not sure about it doing what you describe.

[85_Olds_Ciera]

I have had problems with my car running rough and surging idle..I shut car off to go into store. When started car again, it idled normal with no problems?

Rest of the story? Was it IAC?