Keep turning the throttle stop screw in (clockwise) a 1/4 turn at a time until the motor no longer revs up then idles back down. I noticed this was the case when I adjusted mine when I was reading the IAC on my scantool. For what it's worth, on *MY* car, the throttle stop screw ended up being screwed all the way in when I read 0 on IAC, engine running, in park. You might want to set your TPS at .38 before you start adjusting the IAC, as your TPS will go up as you turn the throttle stop in. Then check/reset the TPS when you're done screwin'.
This ASSumes you are trying to set the IAC to "0". If not, forget what i just said.