Ghostly sound from engine compartment?

[Bottomlesspit]

Hey there. I am still figuring out all my Explorer parts and such but I have a problem I hope to get more info on. Maybe it is normal or someone else has encountered it on their X.
With the engine running I can hear a sound from the engine compartment that sounds just like a ghost howling. WHOOOOOOOOOO. It is just loud enough to hear. If I turn the AC compressor on it gets a good bit louder. The howl changes with rpm.
I have tried to pinpoint the location, but only know it is coming from the top/intake area of the engine. This is not just air coming through the intake hose. You can hear it loud inside and outside the vehicle. It is also not the fan blade.
Anyone encounter this or have some ideas? I am pretty familiar with working on engines, but this 4.0 is new to me. It is all stock.
Thanks,
Ken

 

[Jason_25]

Have you tried a search? The problem is most definitely your IAC valve.

 

[Alec]

Welcome!

Most likely the IAC, idle air control valve. Many threads on this topic, these can be found with the search feature.

 

[Slick Rick]

... It's the ghost from A4LD past.

 

[Abraxsis]

Whoa, I just heard this exact same noise this morning. I drove a 60 mile trip to school and when I arrived I heard the noise while I was sitting at a stop light. It seems to go away when I press the gas or put the vehicle in park. Same thing??

Ill check into the IAC.

 

[Alec]

yup, howling at idle that otherwise goes away is IAC.

 

[Flounder]

IAC is a 60-100 dollar part depending on your year and what dealer you get it from. The installation is a do-it-yourself one: unbolt the old one, bolt on the new one. It's not that bad.

 

[Yng_pnk]

Where is this IAC at?

 

[Alec]

On the intake manifold close to the throttle body. I think it's under your tb cover that says SOHC. 2 bolts, silver cylinder with small black cap and a wire plug.

 

[Bottomlesspit]

Thanks for the replies. Sorry about re-posting a previously hashed out subject. I guess I used the wrong words in the search I did?
I am very familiar with the IAC devices, but not sure I understand just what it is doing in this case. What could a new one possibly cure? The one in our stangs always gummed up and caused a bad idle, but never contributed to noise problems. Is this anything to worry over other than just creating noise pollution?!
Thanks,
Ken

 

[Robert]

Here's a tip for determining if it is your IAC valve. Take a 2' piece of 3/8" tubing and put one end in your ear and put the other end next to your IAC valve when you hear the humming. Use it like a stethoscope (one of those things Alec has to carry around). When I did this the hum coming through my tube made my ear ring it was so loud. Also put it down next to your air filter or air box. You'll hear it there to, just not as loud.

If you don't have any other problems, then a new IAC will only cure the annoying humming. If your idle drops very low (low enough that you think it might die) then that could be a sign that your IAC valve is getting ready to go out. Here's another tip: Try cleanin the IAC valve with Seafoam before replacing it. I bought some syringes from Walgreens (Alec probably gets these for free) and injected about 3 or 4 ounces of seafoam into my IAC valve about a month ago and now there is no signs of the humming. I removed the black filter cap from the side and injected the Seafoam into the metal hole on the side of the vlve. The way I figure it is the valve is getting contaminated with dirt over time. Seafoam is excellen for removing carbon deposits so why not use it for removing sludge in the IAC valve? As a matter of fact the literature that came with my can says it is a great cleaner. Blip the throttle slightly while you are injecting the Seafoam into the IAC valve so it draws it in. A $4.50 can of Seafoam is cheaper than a $60 IAC valve. Worst that can happen is the noise comes back.

 

[Bottomlesspit]

Thanks for all the info Robert. I will give the whole thing a good test. You all keep mentioning a "humming" sound, but mine is a howling sound. Not sure if this might be considered the same sound or not. It sounds like when I was a kid and you made a loud 'whooooo' sound through a paper towel cardboard tube?! Definitely not a hum here.
Thanks again,
Ken

 

[Jason_25]

Yep, same problem, different intepretation.

 

[Alec]

Relating to Robert's post, yes I have lots of cool toys!