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Intake moan, high idle. Could this be EGR or IAC?

9K views 9 replies 4 participants last post by  Floordford 
#1 ·
I posted up about this some time ago but now I want to know, how do I clean the EGR valve and IAC so that I dont damage them? Does anyone know the voltage that would be able to test cycle the IAC so I can see if it is working properly?

This intake moan noise happens within 10 minutes of driving after cold start. It also happens after i let off from a WOT cycle. So the only two units that let air into the intake when the throttle blade are closed are the EGR valve and IAC valve. The PCV valve lets in air but its not consistent with PCV symptoms.
 
#2 ·
Start your car and then unplug your IAC. If your motor dies, your IAC is good.

I believe thats a way you can check to see if its still functioning.
 
#4 ·
it's the iac, quite common failure.

and actually when you unplug the iac it shouldnt stall. it should idle around 550 rpm. if it stalls, clean the throttle body out with some carb spray and recheck. if still stalls turn the idle screw up until you get it to idle without the iac plugged in. This only works for cars without aftermarket cams, but it is the correct way to set it.
 
#6 ·
Update:
I took my IAC off and cleaned it with Sea Foam Deep Creep and an air gun, careful not to get the solenoid part wet. I even cleaned the little felt tablet under the black cap. I also cleaned the hole into the upper plenum and the 3/4" hose and box going from the air tube to the IAC.

I get everything cleaned, dried and installed with care, and did it fix it? No. Now its moaning all the time. Its like I took a baby calf away from its mother. It just moans all the time now. Its an annoying bellowing noise.

So today its off to Advance to get a new unit. So much for spending the time to clean it.
 
#8 ·
I replaced it and was going to add an update. The new unit cleared it up. And it seems to transfer from idle better. Like when I pull it out of gear, the engine doesn't jerk from 1,500 down to 750. it goes down smoother.
 
#9 ·
Sorry, been busy. Yes, it should basically barely idle on its own with the Iac unplugged. Then when you plug the iac in, it will rev up a bit and then settle down.(engine fully warmed up!) If you have a scan tool, you'll see when you set it up this way the iac duty cycle will be between 30-35% which is ideal.
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Some of the ford Iac's had the bellows which also made the same noise but our 96-04 gt stangs do not. SOmetimes after you clean it if you spray a little white grease in the Iac it will get rid of the noise for awhile but it always comes back eventually. I think the shaft gets worn inside there and the noise is created by it rubbing against the housing as it moves back and forth rapidly.
. I would still clean around the throttle blade inside the throttle body. A black gunk builds up around there making the iac have a higher duty cycle to maintain the desired idle speed.
 
#10 ·
Gotcha. I did unplug my IAC to test where my RPS fell because Ive never tested it and I have a good list of mods that could change the idle. Like a ported upper plenum and a 75mm throttle body. My unplugged idle was right at 550rpm.

What was happening when it got worse is that it would idle at 850 with a faint moan. Then it would seem to adjust itself and then the moan got really loud and it would idle at 1300 or so. Then it would lower the idle but drop it too fast. It would drop to 400 and then save itself but then go back to 1300 with the moan. It would just stay in that cycle.
 
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