Pontiac Repair: Rough Idle, 1997 pontiac sunfire, pontiac sunfire

Question
I have recently been restoring a 1997 pontiac sunfire that has ben sitting around my parents for a few years. The original problem was the timing chain, but I ahve replaced that and some other things. It starts up with no issues, turns over fine but the problem is everything runs well when the engine is cold, but when I have had it running for a while or when the engine gets to "normal" running temperature the car will run very rough. It will sputter, hesitate and almost wants to stall. If I turn it off and let it cool down for a while and start it back up again the engine runs fine again. What is the issue. Is it my O2 sensor or ignition coil? Or is it something else?

Answer
ok well what it sounds like it this   upon starting that car the car is in a preset computer mode or open loop.. as it warms up it goes into closed loope sending information back and forth to it, i would geuss that once it warms and goes into a closed loop the computer senses a problem with a controlller or sensor, please have the system checked to see what is failed and replace that unit