Idle Air Control Valve
Freshman User
Joined: Jul 2003
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Idle Air Control Valve
Originally posted by alancp
it sure can make loud noise thru the air filter box, unplug it while motor is running and it will quiet down if it is the IAC
it sure can make loud noise thru the air filter box, unplug it while motor is running and it will quiet down if it is the IAC
I've been getting that humming through the intake too.
I thought it may be the IAC (I've had 5.0 Mustangs in the past and cleaned them yearly). I cleaned it, but the problem didn't go away.
If the IAC failed, would I start getting an off-idle bucking and possibly backfire situation, especially when the car is cold??? I just started getting that problem. I've been at a loss for what it could be.
I'm also not getting a check engine light. It amazes me that I could get that bucking/sputtering at lighter throttles pressures yet not trip some sort of check engine light reading.
New User
Joined: Jul 2003
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Idle Air Control Valve
Does anyone in this thread know the procedures to disassembly & reassembly the IAC valve? What tools are needed? What products are required to clean it? I will appreciate your comments and observations on this matter
Post Fiend
Joined: Jan 2003
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From: Connecticut
Idle Air Control Valve
Hi caribe, welcome to FTE!
You cannot take apart the IAC. You can only take it off the engine to clean it, and you do that by unbolting the two bolts that hold it on to the upper intake. Then you can clean it with throttle body cleaner spray which you can find at your local auto parts store. What you're trying to do is dissolve and remove any carbon and dirt that has built up inside the unit.
Keep in mind that sometimes cleaning the IAC helps, sometimes it doesn't.
You cannot take apart the IAC. You can only take it off the engine to clean it, and you do that by unbolting the two bolts that hold it on to the upper intake. Then you can clean it with throttle body cleaner spray which you can find at your local auto parts store. What you're trying to do is dissolve and remove any carbon and dirt that has built up inside the unit.
Keep in mind that sometimes cleaning the IAC helps, sometimes it doesn't.
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Idle Air Control Valve
Like was mentioned earlier... cleaning doesn't always fix it.
I just replaced mine ($84 from Ford, while I saw on the screen their cost was half that!), and it made the screeching sound go away. I cleaned it Saturday and it didn't help.
Now I need to figure out my hesitation problem!
I just replaced mine ($84 from Ford, while I saw on the screen their cost was half that!), and it made the screeching sound go away. I cleaned it Saturday and it didn't help.
Now I need to figure out my hesitation problem!
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Logistics Pro
Joined: Sep 2002
Posts: 4,410
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From: Central KY
Idle Air Control Valve
Thanks Rockledge, your NAPA part number was correct. I now have a new IAC valve on the way for my truck (they had to order it). It's costing me $48 (family discount 
). I'll let you know how it works after I put it on tomorrow.
). I'll let you know how it works after I put it on tomorrow.
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Logistics Pro
Joined: Sep 2002
Posts: 4,410
Likes: 1,015
From: Central KY
Idle Air Control Valve
Picked up my new IAC valve. It came with the gasket in the box. I took my old one off, it was FULL of carbon. It was absolutely nasty inside. I installed the new gasket and bolted the new IAC right up. Plugged the wiring harness back in, started the truck. Instantly I noticed a much quieter engine. It purrs like a kitten again. Thanks to Rockledge and all who helped.
Thanks to Rockledge and all who helped.
Posting Guru
Joined: Feb 2001
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Idle Air Control Valve
What Ford manual do you have? I use a HELM Ford manual from the dealer and it doesn't show pictures like that.
Originally posted by Rockledge
Here is some more information on the IAC out of my Ford Manual:
Idle Air Control Valve
The idle air control (IAC) valve assembly controls engine idle speed and provides a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air. The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm. The IAC valve [is also] part of the throttle body assembly...
The PCM uses the IAC valve assembly to control:
- No touch start
- Cold engine fast idle for rapid warm-up
- Idle (corrects for engine load)
- Stumble or stalling on deceleration (provides a dashpot function)
- Over-temperature idle boost.
And here is a nice diagram of a typical IAC:
Here is some more information on the IAC out of my Ford Manual:
Idle Air Control Valve
The idle air control (IAC) valve assembly controls engine idle speed and provides a dashpot function. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The PCM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning the IAC valve to control the amount of bypassed air. The PCM monitors engine rpm and increases or decreases the IAC duty cycle in order to achieve the desired rpm. The IAC valve [is also] part of the throttle body assembly...
The PCM uses the IAC valve assembly to control:
- No touch start
- Cold engine fast idle for rapid warm-up
- Idle (corrects for engine load)
- Stumble or stalling on deceleration (provides a dashpot function)
- Over-temperature idle boost.
And here is a nice diagram of a typical IAC:
Post Fiend
Joined: Jan 2003
Posts: 9,748
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From: Connecticut
Idle Air Control Valve
I've got a 1998 Ford Factory Workshop Manual CD (Trucks) and that information and diagram of the IAC I posted comes out of the Powertrain Control/Emissions Diagnosis (PCED) part of the Manual.
However, I actually edited the image of the IAC before I posted it by adding the box that contains the harness connection information.
However, I actually edited the image of the IAC before I posted it by adding the box that contains the harness connection information.
Last edited by Rockledge; Jul 31, 2003 at 09:36 AM.
Posting Guru
Joined: Feb 2001
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Idle Air Control Valve
Someone gave me a 99 ford manual on CD. I guess I will try and see if it has the same pictures. I thought maybe I bought defective Helm manuals. Maybe thats why it was so cheap on ebay. 
thanks
thanks
New User
Joined: Aug 2003
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Idle Air Control Valve
The Dealership just told me I need a new IAC valve in my 98 Ranger XLT 4.OL and I wanted to know if this is something I can handle replacing myself. From the picture it doesn't look like it would take much and the dealership wants $224.06 to replace it. If anyone could let me know I would greatly appreciate it. Thanks!
Post Fiend
Joined: Jan 2003
Posts: 9,748
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From: Connecticut
Idle Air Control Valve
Hello, welcome to FTE!
You can indeed handle it yourself, it's very easy....you simply take off the electrical connector going to the IAC, loosen the two bolts that fasten it two the motor, and then replace the unit with a new one.
However, before you do switch, take off the cable going to the negative lead on your battery...you want to make sure it stays off for about 20 minutes so that the truck's computer resets. Then you need to drive around for a while with the new IAC and the computer will re-learn new values for your idle and store them.
Good luck!
You can indeed handle it yourself, it's very easy....you simply take off the electrical connector going to the IAC, loosen the two bolts that fasten it two the motor, and then replace the unit with a new one.
However, before you do switch, take off the cable going to the negative lead on your battery...you want to make sure it stays off for about 20 minutes so that the truck's computer resets. Then you need to drive around for a while with the new IAC and the computer will re-learn new values for your idle and store them.
Good luck!
