Normally the idle screw doesn't need to be adjusted. It's set at the factory and covered by a brass insert so that it can not be tampered with.
I had to adjust mine after a rebuilt my engine. I had the throttle body bored out. When I got it back, the brass cover was missing. I has an erratic idle that I couldn't find the solution to. After a search, I found this thread.http://www.fiero.nl/forum/Forum2/HTML/080905.html
The sixth post describes a method to set the idle screw. I followed that procedure and haven't had any problems with the idling since.
If the brass idle screw cover is still on your car, then the idle screw setting is probably not the issue. You probably have a bad sensor or iac valve.