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Idle Control Valve "Buzz/Hum"

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996 1999 C2.

Is it normal for the idle control valve to hum/buzz loudly and get warm to the touch when the key is on, but the car is not running?

I noticed it today without the car running - the ICV has a very loud hum to it.

The idle is fine on the car, exept it does vary a little for the first few seconds at cold startup.

Trying to avoid replacing this expensive part unless the buzzing indicates impending failure.

996 606 160 01



Edited by logray
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  • 9 months later...

EDIT: using the PST2 I activated the IACV test and could see the valve close, open, close, open without much force. So I don't think that's the problem. Something else is going on here. Might be fuel pressure related? Strange though that no codes are thrown.

Help !!!

I removed the throttle body and idle control valve like I normally do for a regular cleaning today. I didn't use any chemicals.

I think the ICV might have finally bit the dust ???

Car won't idle at all now!!! On a cold start it just goes to about 1k rpm and then extremely rough up and down to 500 before I turn the key off (avoiding a stall).

I triple checked all of the boots and seals and everything was tight, no intake leaks that I could see.

No DME codes are thrown at all !!!!

The throttle plate angle sensor reads 0 at no gas, and 70 at WOT. Half way is appx 35...

I removed the ICV again and tested it with a 9v battery. The battery opens and closes the valve inside effortlessly and instantly, without any audible hum or buzz.

With the ignition on and ICV plugged in it still buzzes/hums loudly and warm to the touch if I leave the ignition on long enough. The buzzing/humming is even more pronounced when it is in my hand unbolted from the TB.

I tried resetting the DME by disconnecting the battery for a while. No luck.

I also tried unplugging the MAF.

No changes with either of those...

Any other ideas here before I fire off an order for a very expensive ICV? Would the ICV really produce such an erratic idle and finally let the engine stall?

Edited by logray
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Ok, repeated the unplugging MAF test, might have been out of sequence. Now it starts and idles. It sounds OK, but the idle is very rough. I'm going to try to clean the MAF to see if that helps. At least if it is the MAF, that's much less expensive than a new IACV.

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Yep! You got it right! Thanks!!!! :-)

I took TB off again and noticed somehow I dislodged one of the rubber boots next to the y plenum. Just enough to create a small air leak.

Once I sorted that out and tightened the clamps for the y-plenum the car is back to it's slightly wobbling idle 996 self. :rolleyes:

A tip for anyone that happens to read this thread, regarding the y plenum behind the throttle body. You can make sure it is perfectly aligned by feeling inside. Your fingers will be able to "see" that the plenum is centered correctly and there are no gaps in the rubber that joins it to the intake manifold.

And now I've got a clean MAF, which I hadn't planned on touching.


Edited by logray
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