Idle drop in 1991 Buick Park Avenue

I have a 91 Buick park Ave that is experiencing these symptoms.

When starting from a cold start the engine will turn over, reach around 1000 rpm, then die.

When applying gas and turning the key the engine revs up and idles at a higher rpm (say 3000) once gas is released the engine dies.

If the gas is held the engine will cycle through a couple different rpms. For 5 to 6 seconds it will idle at the higher rpm (say 3000) then drop 1000 rpm for 2-3 seconds (down to 2000 rpm) then back up to the higher rpm (3000) for 5-6 more seconds.

The problem is in the Idle Air Control Valve not working consistently. I’ve replaced the IAC. It is supposed to behave by traveling out when given power and in when the power is cut. The out behavior works fine while the in behavior is sporadic.

I’ve tried replacing the ECU, IAC, TPS, and the O2 sensor. There are no continuity issues or vacuum leaks.

Any ideas would be helpful.