Iac has nothing to do with fluctuating idle if you dont believe me unplug it and youll find out anyways I found out my injectors needed cleaned with mine but also what can do it is the mass airflow cleaner may need to be cleaned alittle spray from your auto parts store can help a whole lot.
other than that i have had issues with fluctuating fuel pumps lol
but to figure it out for yourself unplug sensors until it works normal.
Dont overthink things it only drives you crazy