YotaTech Forums - View Single Post - 22RE I.A.C. Valve?? Where is it, and what's it look like??

thook · 04-22-2008, 10:06 AM

The real way to test the IAC valve is when it's cold and hot.

In case you didn't know, it's an auxiliary/supplementary air valve that is suppose to remain open until coolant warms to operating temp thereby allowing extra air past the closed throttle plate in order the speed up the idle. As the coolant heats, and since the valve is thermo regulated, it's supposed to close slowing the idle down. So, if you understand that, you test by adjusting idle speed bypass screw all the way in shutting off the only other source for idle air.

Begin by starting the motor cold. Turning the idle screw in should only drop the idle down to around 100rpm. At this point, the open IAC is the only source for air. Turn the screw back out and let the engine warm. (At this point, the idle speed should've dropped to the 750 idle speed, anyway.) But, if not, turn the idle screw in and the idle should drop below 100rpm. If there's no difference from the cold fast idle, likely the valve is stuck open. This is what can cause surging....too much air to fuel ratio. Fuel is supposed to lean out when the coolant temp sensor resistance drops from rising coolant heat. (Which, btw, can also cause surging....a bad sensor, that is)

If, on the other hand, the valve is stuck closed (usually the case) or the air passage is just clogged, you will have no cold fast idle and the truck will barely run.

If you do have a cold fast idle, the IAC or auxiliary air valve (as Toyota calls it on early models) is not your problem and testing the valve is pointless.