IAC Question

[AZGunner]

Hello all,
I have a '93 Festiva GL automatic that recently started having idle issues. I think that I have tracked the problem down to a faulty Idle Air Control unit. When I removed the IAC there is a hole on the back that I cannot figure out what goes there. I am thinking that it should be plugged, so I went ahead and did that. Now the car idles very high. I have not measured it with a tach but I would guess maybe 1300-1500 rpm. When I unhook the electrical plug at the top of the IAC the idle does come down somewhat but not to the 8-900 rpm's that it should be...even after warmup. So my question is, should that hole on the back of the IAC have a plug there? It doesn't make sense to me to have vacuum hoses running off of the IAC with a hole at the bottom. And why are the rpm's lower when I unplug the controller? I have the idle screw turned all the way in and rpm's are still too high. I have tried finding a vacuum leak but I don't see any hoses that aren't hooked up. I guess next step would be to clean the VAC but I'm kind of stuck as to what to do next. Any help from the Borg would be greatly appreciated.
-AZG

[Movin]

If your engine backfires pretty hard it can blow a little cap that is crimped in place into orbit! The same backfire can change clearances in the VAF and cause variations from normal with the sensor values reported to the computer.

it can also cause hard to find vacuum leaks in weird area's. If the throttle is open a little it can cause air leaks between the throttle body and the VAF.

Air leaks and vacuum leaks can be found easy with an unlit propane torch whiffed around possible area's while the car is idling. A change in idle indicates a leak. Carb cleaner sprayed in the same manner will work the same.

There are pieces inside the idle air control that may be missing. The valve can be capped off and removed, the idle is then set with the screw on the throttle body instead of using it to set the minimum idle air flow.

Be careful, these test methods are very effective at finding spark plug wire shorts or other sources of ignition. Eyebrows might be the least of your worries

Welcome to the site!!

[rmoltis]

Lol that's funny the propane thing
What a great idea.

[Bert]

Movin's suggestion of using an unlit propane torch to test for leaks is a beautiful one. I used this many years ago to confirm that there was an intake manifold gasket leak on my truck. With the propane on (just a little bit!) and slowly and carefully directed along the manifold the engine suddenly went from running rough to running smooth.
This lo-tech technique works like a proverbial charm and even allows you to pinpoint exactly where the problem is.
It's good to be reminded of simple tricks every now and again! Thanks Movin.