MustangJilly

Ok really need some help!! I have a 2002 Mustang GT 4.6. The current problem is that it wants to idle between 1200 and 1300 RPMs. When it is hung in this idle it has a loud humming noise then it will lose RPM's and shut off. I have a new IAC on it so I know that is not the issue. Has anyone else had this problem??

CalBoy101

To make 100% sure its not the IAC try unplugging the connector and also pulling the big hose off the front of the valve and blocking it closed while its running, even though its new it could still be hanging open.

If that doesn't change the rpm its probably got a vacuum leak, lean over with your ear and see if you can hear where its coming from. A short piece of hose up to your ear can help with this process by moving the hose around to find where the noise is coming from.

MustangJilly

It sounds like it is coming from the same area the air filter is in. It is so strange and I can not seem to figure out what it is. Someone told me it sounded like my smog pump was clogged the only issue there is I am pretty sure it does not have a smog pump....

JJ Glo

The loud humming is the IAC, it is failing. When that happens, the sound will resonate all of the way to the air filter box, believe me, I've had this happen with two IACs in the past few months.

What brand IAC did you get?

MustangJilly

To be honest I am not sure. A friend went and got it for me. I will get a new one do you have a recomendation on a brand?

CalBoy101

Before you buy another IAC do the tests I recommended, while the engine is running pull the electrical connector of the IAC, the engine should go to very low idle when you do that. Also pull the big hose almost all the way of the IAC, start the engine, then pop the hose off and cover the IAC inlet with your hand, again the engine should go to very low idle.

Also the black plastic box that is inline with the hose that goes to the IAC sometimes can get cracks in it that can cause vacuum leak problems, take a close look at it. Its just a resonator (its supposed to eliminate "hum" noises) so it can be removed, i don't think you can buy replacements for it anymore.

antwaan

Sorry to slightly thread jack but I was working on my car last night and have had idle issues. I recently replaced my IAC and while the car runs better I still get hanging (more like stuck) rpms, but less frequent. I had the car running and unplugged the IAC and got no change in idle. Its a new IAC, what would that mean? Can an exhaust leak cause that problem? Because I seem to have a leak at the passenger side manifold and I'm getting a lean bank one code. I plan on fixing that in the winter along with some other possible major work but not yet.

JJ Glo

With the IAC, you should really only buy Motorcraft. I have gone through two Duralast in the past few months, the first one only lasted 3 weeks, wish I had known sooner.

You can get a motorcraft on Amazon for about the same you can get a Duralast from Autozone and the Motorcraft comes with a 12 month warranty.

CalBoy101

Normally when you unplug the IAC this forces it to close and the engine should drop to a low idle or even stall.

If that's not happening you could have a vacuum leak that's letting in extra air or your throttle body could be worn and letting more air go by than it should when its closed.

Try shutting the car off, pulling the big hose off the IAC and plug both the IAC inlet and the hose outlet and then seeing if the car still idles high. If it still idles high air is getting in somewhere else and you need to figure out where, if not your IAC is flakey.

MustangJilly

Ok so I replaced the IAC cause nothing else worked. The humming is gone bit now every so often it wants to idle really high when I push in the clutch to change gears. It that normal? Also someone told me to run a can of seafoam through the brake booster vaccum line while having someone hold the gas pedal. Has anyone ever heard of that? Thanks again for helping.