NEED Big help with 92 3.1L Engine Hesitation Please

Hey everyone!
I have a 92 Cav 3.1L With over 300K KM on it.
I'm not sure of the service record of the vehicle, however since we've gotten the car it has develloped a drivability problem. The car backfires as you try to start it, upon starting the car it usually runs well, but once it is warm the car begins to hesitate severly, sputter, or completely stall. Giving the car more/less throttle does not help the car, and in fact, when the car does this it almost does not recognize throttle input at all. I have a feeling it's sensor related, but don't know enough about the engine to know what to test or what to look at. The oil pressure gague also tends to go real funky and sways back and forth when this happens. We have replaced the plugs and the O2 sensor to no avail. I have heard of this being a cat. converter problem, however there seems to be no flow problems.
Any help would be great to help the car roll closer to the 1M KM Mark. Thanks!

Well seems to me that the IAC Idle Air Control Valve is not working, just replace it and you should be fine if that fails you need a new ECM computer.

This may not sound right but bear with. Mine also has 300K on it and it started running rough. What it was is a hole in the rad cap caused the rad to suck air into the system. When this occured air pockets in the system would hit a coolant temperature sensor and trick the computer into thinking that it was -20 F and the computer would richen up the mixture to warm up the engine. The fix is to go to a 20 min oil change shop and get a rad flush and to get a new rad cap.

The suggestion on the Idle Air Control valve is a good start. If you replace that and the car still wants to do what its doing, I would suggest replaceing the Ignition Module or coils. They tend to go bad overtime causeing some really strange things to happen with starting, idleing or drivein in general.