My car runs smooth when it is cold.Idle is a bit high, When the engine starts to warm up and the idle starts to drop it runs rough and sometimes stalls. What is happening when these cars go into closed loop? I guess thats what is happening right. Car is 5.7 89 GTA

 

when the car gets into closed loop, the computer starts taking info from the sensors and starts making adjustments to how much fuel is getting sent to the cylinders. so hook her up to a scanner and watch what the computer is seeing. sounds like a senor isnt working like it should

 

like scottsz28 said, once in closed loop the ECM starts taking feedback from all of the sensors and adjusts timing/fuel/EGR/ect as required.

could be a sensor, wiring or maybe something as simple as a broken ground wire somewhere. Bad grounds can cause some pretty freaking strange stuff!