Clean out the idle air control valve, check throttle position sensor voltage also. Carbon build up in the IACV will keep the plunger from moving, if it's vacuum controlled check the hoses and check valve for leaks, if it's electric, you can turn the car on to run, (not running) with the IACV un-mounted, open the throttle blade a few times and see if the plunger actuates, if not replace it. I think you're on the right track.