1992 Cutlass Supreme Idling Issues

Hello Everyone! I'm glad I found this forum.
I have a 1992 Cutlass Supreme S, with the 3.1 engine. Car has 190K miles on it and well maintained.

Car seems like its searching for idle at low speed and stop lights and the RPM's will go up and down, and surge. I replaced the Coolant Temp. sensor and that has not solved the problem. Checked for vacuum leaks and fuel pressure is fine. Also, I disconnected the TCC solenoid connector to see if that would resolve the issue and it did not. I'm down to the O2 sensor and the Idle air control valve and possibly the throttle position sensor. Which is the likely cause? Also, I was advised to clean the Throttle plate. Any other suggestions?

EDIT: Also wanted to add that it idles fine in park and neutral. I will put it in neutral at stop lights if I think the car will stall out. Additionally, it generally happens on a warm engine.

Welcome to AF, keep looking for minor vacuum leaks, stop randomly replacing parts. Remove te the EGR and clean it, clean the throttle body, clean the iac, scan it for sensor input anomolies., alll part of the diagnostic process.

Good post! I will have a friend run a scan this weekend to check for error codes. Where is the IAC located and what is the best way to clean it?

On the throttle body, metallic looking cannister, check autozone.com, repair guides for some info.