Start with taking a look at the air intake system, have a look if there are any air leaks from the airfilter to the intake manifold.
If this is alright, check out the air mass sensor, throttle position sensor and the idle control valve.

yep, iac is normally the culprit with this one let us know as to your progress


insted of picking up another one, remove it and clean out the inside and see if it makes any difference


you can use brake cleaner(aerosol spray) and some wd40(maybe a rag and a q-tip) but make sure its dry before you replace it