1990 Chevy Beretta Low idle, likes t cut off.

I have worked for gm for a long time and this engine 2.8w or 3.1t engines are very tricky to get to idle perfectly. The gm scan tool called a tech1 has a program in it to reset the idle air control valve. First of all you have to start with a clean throttle bore and tps voltage at close to.68 volts with a throttle angle of 0. If you have access to a scan tool you can check the tps voltage and set it as close as you can and if it shows a throttle angle at all, you can reset it to zero by disconnecting battery once you have the correct tps adjustment. They only used this system for a few years then they changed designs.