During idle, the proper position of the iac pintle is calculated by the pcm based on battery voltage, coolant temp, engine load, and rpm'*. If the rpm'* drop below a specified value, and the throttle plate is closed, the PCM senses a near stall condition. the PCM will then calculate a new IAC pintle valve position to prevent stalls.
If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset.
The IAC resets when the engine is started, runs over 800 RPM, and then turns off.
The position of the IAC pintle valve affects the engine start up and the idle characteristics of the vehicle. If it is open fully, too much air will be allowed into the manifold. This results in a high idle speed along with possible hard starting and lean AFRE. If the valve is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed along with possible hard starting and a rich AFR. If it is stuck part way open, the idle may be high or low, and will not respond to changes in engine load.
From the 1993 GM service manual. Pardon typos, I'm not proofreading my typing.
The scan tool displays the IAC position in counts. Zero counts indicates the PCM is commanding the IAC to be driven all the way into a fully seated position. This is usually caused bya vacuum leak. The higher the number of counts, the more air is being commanded to bypass the IAC pintle.
I have the book open to the IAC diagnostics. What are your EXACT symptoms causing you to suspect he IAC?