Help idling issue... have tried various things

[enixxi]

Hey, I have an s13 with a redtop sr20, blitz fmic, 3 in turbo back. I just moved to arizona and drove the car (http://zilvia.net/f/) all the way out with no issue, but after a few days my car's idle started stumbling. What would happen is I would drive the car around normally untill around operating temp. which according to the gauge is under 80 C. Once it was warmed up it would run and boost fine, but the idle would stumble and the car would shut down. It would fluctuate between 0-900 rpm almost shutting down or actually shutting off.

At this point I tightened up all the intercooler piping, replaced the vacuum hoses and made sure my maf sensor was well grounded. After the intercooler piping and vacuum hoses were replaced the car stopped shutting down. Now 3 different things can happen when the car is idling.

1) It idles fine
2) The rpm drops to about 200-300rpm and my fpr gauge reads 10.0
3) the rpm fluctuates between 0-900 rpm almost shutting off, but barely staying on

These symptoms occur randomly during the same driving session with the fluctuating idle being the most common. The last thing I've tried is switching O2 sensor's (http://zilvia.net/f/) with my buddy's O2 sensor and the same thing still happens. Has anyone had similar problems or have an idea as to what can be wrong?

[RBPowerSilvia]

next time this happens unplug your mass air flow and see if your idle goes back to normal. i would also not rule out the possability of a vacuum leak, get a intercooler coupling that you dont really need and put a valve stem in it. then put the coupling you just made on your piping somewhere where it is easiest to get to with air hose and pressurize your system. DO NOT PUT TOO MUCH PRESSURE IN YOUR SYSTEM THOUGH listen for leaks. ---also did you try taking your idle air control valve off and swapping it with another one?

[enixxi]

So I just cleaned my IACV and the car hasn't had a stumble since... I've only driven it for 10 min and sometimes it didn't develop until a little after, but I'm going to the gym in a little bit so that will be the true test. Can't believe I completely overlooked the IACV before this...