Ok guys...lately as you know my truck has been making a LOUD humming noise at idle when the engine is warm. Over at The Ranger Station, some other guys say their 4.0L does the same thing. It is VERY loud, and today when it happened I popped the hood, took the air box apart, and the noise got even louder. So it has something to do with the air flow into the engine.
It was suggested to me to try a new IAC. That is the Idle Air Control valve, right? Because I checked four different auto parts stores, and none of them have an IAC listed for my truck. Only Autozone has something they call an "Idle Air Bypass" for my truck, and it's $132.00!! Can somebody help me? All I have is the Haynes manual, and it's worthless of course.
Hmm..thats curious that NAPA online doesn't even list one for my truck. And Autozone lists them for $122.00. I think I'll try cleaning mine first. If that doesn't work I'll try to find one of those cheap ones you guys found.
Thanks much for the information, and thanks Rockledge for the picture!
By the way, can that thing make loud annoying noises at the air filter box?
I had to replace my (98 4.0L) IAC valve last year, only 60-something dollars at the dealer, only took a few minutes to install although as mentioned you may just be able to clean it. My truck sounded like a foghorn whenever I was stopped in traffic or at a light..
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)
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