The IAC screw should never need to be adjusted beyond the factory setting boss. If its set to high stopping the car will be a problem. Check your tps voltage on the scanmaster at idle or key on. .38 to .45 is where it needs to be. WOT needs to be between 4.2 to 4.8. Don't exceed 5 volts. IAC counts at idle 10-20. If it's not high enough it will stall. Adjust the IAC first then the TPS Voltage. I stress again to high of a IAC setting will cause the engine to not kick down and hinder slowing down not to mention it will jump forward once in gear. Post the scanmaster numbers and we will walk you through it if needed.