Idle Reset Procedure
Here is the correct procedure to set and adj the idle. No guess and check crap and it works 100% of the time.

1. Disconnect the battery terminals to reset/clear the computer's memory. Leave it disconnected for 30 minutes. WARNING: Whenever removing your battery cables ALWAYS disconnect the negative battery cable first and reconnect it last. Otherwise you could destroy your computer or cause a battery explosion.
2. Disconnect the plug going to your idle motor which is located on the front of your throttle body.
3. Reconnect your battery's positive and then negative terminal.
4. Start the engine, and set the idle to the rpm you want with the stop screw on the bottom of the throttle body around 750-800rpm is factory spec.
5. Turn off the engine.
6. Check the TPS and adj. the voltage if necessary to be btw .94-.98V with the Key On Engine Off.
7. Reconnect the plug on the idle motor
8. Make sure all accesories (radio, blower motor, a/c, lights, etc) are off and start the engine.
9. Let engine run for two minutes.
10. Turn engine off and wait two minutes then restart engine and let idle for two minutes with all accesories on.


Take a look at this link and it explains cleaning the IAC adj. the TPS and a few other things to fix a surging idle. http://www.muscularmustangs.com/iac.html