Idle Air Control confusion please help

Ruddell

Member
I recently installed a new IAC on one Ty (GM 17112193) and was still left with no idle. Long story short, I bought another one and it's been running fine ever since. So the thing was clearly defective. The first one I installed had no sound coming from it with the key up. The second one had a nice humming sound. And this is the one that ended up working.

I did follow the reset instructions. Ground A&B with key on, wait 30 seconds, unplug IAC. Key down, unground terminal. Start truck. Shut off truck. Plug IAC back in.

So my other Ty also has a stalling and no start issue. It has good fuel pressure and spark. I put in a new Ac Delco ICM. Next I decided to go ahead and put in a fresh IAC. I installed it and got to the point where I did the reset steps, the IAC was making a humming sound, and it started up and ran for two minutes then shut off. It will not start again.

I noticed the IAC is now making a very faint click type sound deep within. What's that about? I plugged in two other ones and it does the same thing. I am very confused. Are they all defective?

Another thing i noticed is when I ground the terminals, it is not giving me the check engine light. What could cause this?

Thanks in advance.
 

Ruddell

Member
As it turns out, the IAC is not faulty. I ended up getting it to work only after the ECM provided the proper signal to the plug and allowed the truck to start up. I do however have a entirely different problem to figure out regarding the check engine light not coming on with the key up...
 
Hey Ruddell,

The clicking you hear upon turning the key to the on position (not start) is most likely the IAC attempting to close, when it is already in the closed position. That faint clicking sound is the IAC working against itself to close.

I highly suggest reading this post by the user VADER here. You'll have to scroll down past the original question, but it is the second post in that link.

He gives a great general explanation on how to, in my opinion, properly service an IAC, as well as an overall great description of what exactly is going on when it makes that clicking sound. Hopefully it helps to explain what the IAC is doing at the least.
 
There used to be a pretty good IAC post from Daron on here back in the day. It may still be here somewhere. I'll have to see if I can find it.

Edit: Nevermind. Pretty sure it was a TPS post. Not IAC. Sorry about that!
 
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