2000 Impala 3.4L idle problem

This car has 250,000 miles and has been pretty solid. Recently, I have been having an idle issue in that unless I keep my foot on the pedal, it will stall. I cleaned the throttle body and all the ancillary add-ons yesterday and did not resolve the problem. I was left with simple adjusting the idle screw to raise the RPMs. Easy fix, but I thought the engine controls/computer would make any adjustments needed. So I feel that what ever the problem is, it has not gone away. BTW, there are no codes and no CEL so no clues there. Any suggestions?

Get that base idle screw back where it was that is factory preset, the tps will have skewed inputs as a result, remove the iac and clean it and the passages, make sure the egr full seats also.

By increasing idle with idle screw, I bet that tranny jumps in gear or has a harsh feel when put into drive....

Hard to believe no codes are set......I have a tool that attaches to the IAC to make it increase and decrease idle, to check the IAC....a bi-directional scan tool is better, since you can increase/decrease idle via the IAC through the PCM....

It's possible the IAC is bad, or the circuit to it is bad, or you have a PCM problem....

These days, it's almost impossible to diagnose problems without a scan tool, even if it's not bi-directional....you can see the rpms and also see the IAC counts, to see if the PCM is commanding the IAC open.....

Have seen this on a couple. Try starting the car and play with the connection at the MAP sensor thats what it was on mine. Worth a try

I just wanted to close this thread and thank you for your suggestions. The ultimate fix was replacing the IAC. Everything is set back to original settings and all is well!