1996 Chevy Cavalier Car idles normal until slightly warmed

I just repurchased this car back from a guy I work with and I can't seem to find the problem. This is the 2.2 OHV engine and there have been extensive performance mods that I had done to it originally such as porting the head, intake, header, exhaust, etc. When I owned the car I never had any issue with it, but now when you start the car up it will start as normal and idle just fine until the engine is warmed up a little and goes into closed loop. Once in closed loop the engine will idle down to a near stall then rev itself back up, fall down again, rev back up over and over. If you give it gas it will sputter extremely badly until it gets near 3k rpm then it sounds like it clears out.

I have done a compression test and the numbers are not great, but not out of spec. I've replaced the front o2 sensor, checked the Intake temp sensor, EGR valve, spark plugs are good and the same for the wires. There's no blockage in the exhaust system as I have removed the cat for testing reasons. The only code that is coming up is the secondary o2 sensor, which makes sense since there is no cat right now, but that wouldn't cause the problem anyway.

Just at a loss right now, not sure if maybe the ECU is fried, or maybe another sensor such as the ECT perhaps?