Should my truck die when I unplug the IAC while it's running if the IAC is working properly? Thanks.

 

As far as my understanding goes, the truck won't necessarily die. If anything, it'll idle higher with it unplugged, and the idle may jump up and down.

If you're experiencing idle issues, try taking it off and cleaning it with carb cleaner and a toothbrush before you replace it. There's a few good posts here on that topic, use the search tool and you should find a few writeups on cleaning it.

If there's no change from there, you may have a vacuum leak. Try some propane enrichment and see if you can find anything.

 

The IAC solenoid plunger is opened and it's position controlled to maintain constant idle speed as accessory loads change (A/C, blower, lights, etc.).

When starting the engine, it opens to maximum to allow as much air as possible into the cranking engine; the PCM then allows injection of excess fuel to get started and running. As the engine catches and starts running, the IAC closes down to control air flow for idle.

The IAC valve bypasses the throttle plate, with a passage allowing air flow around it. If the IAC solenoid is disconnected, the valve will remain closed, and the engine will suck in whatever air can pass around the closed throttle plate, usually not enough to keep running. imp

 

It won't always die, it could have the same effect as when you disconnect the vacuum hose. it would idle waaaay low. not saying it couldn't die though. anything is possible

 

Here's the deal. The IAC valve is run by a stepper motor. On engine start up it cranks to closed then opens a predetermined number of clicks. Once in open loop it opens slightly when the throttle is suddenly closed to prevent bounce back and allow for smooth operation. At warm idle it is controlled by the O2 sensor and the EEC. If you disconnect the wire it will stop adjusting wherever it is.

 

Ya got this way out of whack. No IAC was EVER run by a "stepper motor". Before "drive by wire" protocol, the IAC consisted of a solenoid-operated air valve, mounted in parallel across the throttle plate. This allowed control of the AMOUNT of air entering the engine, with FOOT off the gas pedal. During engine cranking, the IAC was FULLY OPEN, injectors fed LOTS of fuel, to get the damn thing to fire. Quickly after the PCM learned the crankshaft was spinning, it slowly closed down the IAC while feeding less and less fuel, while "watching" eng. rpms.

With "drive by wire", the throttle plate is DRIVEN by a motor, call it a "stepper" if you like, which SLIGHTLY OPENS the throttle plate while cranking, then slowly closes down the plate after the engine "catches" and normal idle speed is obtained.

Drive by wire takes away the driver's option of "mashing" the gas pedal whenever he wants to. That is, if PCM detects some kind of problem, like, oil too hot, coolant too hot, transmission malfunction, cylinder misfire, exhaust gas stream emissions way too high, it will not allow for maximum eng. power output, no matter if you push the pedal through the floor.

In other words, the computer NOW runs the engine as IT sees fit, given certain degrees of latitude to the driver. imp

 

Sorry you are correct. I was thinking of electronic.( fly by wire ). Thanks for the catch.

 

So if the IAC is working correctly, when I first start the truck it should idle high (around 1200 rpms) for a few seconds then slowly decrease until it gets to about 700 rpms? That's what my truck does.

 

That's normal. If it stays high or low for a long time or excessively revs up and down you may have an issue.