Civic Idle Problem

I have a 97 Civic stock 1.6 non vtec and im having problem with the idle. When the car warms up and when im only in park or nutural, the idle goes up and down in between 500 and 1100 rpm. When i take and plug the IAC (idle air control valve) inlet hole the engine runs fine. Any suggestions on what the problem is. I tested foe an intake leak w/ propain. Any help will be great. Thanks

it could be that the iac is messed up or u have some dirt in that area try to clean it up see what happens and if not try diagnosing it see what ecu codes u get

I put the intake cleaner to it and it diden't clean it out yet. I got the code for the iac once and then i have a studder while i take of in gear. i cleared it with the scanner and it hasen't done it yet. but the flux is still only in park and nutural.