Loud Noise From Intake Manifold

What kind of noise is it?

Popping? Hissing? Whining? Sucking? .....

Dave

It's a loud sucking noise similar to a vacume cleaner.

I actually removed the air filter housing and replaced it with a K&N filter. No more housing. Noise still there.

Will probably have to take it to the dealer. I'm sure they'll tell me it can be fixed for a mere $1,000. I've already dropped $4500 into the vehicle this year. Had to have the tranny rebuilt and the master cylindar replaced along with other minor work. Might be time to get rid of this puppy.

I recently had to replace my IAC valve. After my "cleaning" it to try and remedy a different problem, it started to "moan" at idle. I suppose the sound could be compared to a vacuum cleaner - not the swoosh of rushing of air sound, but the droning sound of a shop vac, although at a lower key. The IAC still worked ok, e.g. the engine still idled fine, but the noise was major irritating. It would disappear during cruise, but would usually reappear at idle. Seem to remember reading in past posts that the IAC can cause this noise. The new one was about $45, 5 minute job to replace, sound gone for good. '96 XLT 90k miles.

Thanks for the info. Will look into it. What is an IAC?

IAC = Idle Air Control. It's an electrically controlled valve that allows air to bypass the closed throttle plate at idle (and thus keep the engine running), and is controlled by the PCM (powertrain control module). It's cycled opened and closed by the engine computer to maintain a set engine idle speed. Sometimes called Air Bypass Valve. On my '96 its little cylindrical looking thing located on the upper drivers side of the throttle body, mounted with two bolts and has an electrical connector attached.

Mine was fine until the second time I tried to clean it, after which it started making a kind of a moaning noise during idle. Think I went overboard on the cleaning fluid, and got it up into the electrical part of the valve. After driving a bit it stopped making the noise for a minute or two, but as soon as I snapped the throttle shut it would start again. I only drove it that way about 10 miles before I replaced it. But in my case, since the noise didn't start until after I monkeyed around with things, and since I knew the IAC was what I was messing with, it was pretty easy to guess what was causing the noise. Since I had almost replaced it a year earlier due to idle problems in the winter (the first cleaning fixed that), I figured the thing was already on borrowed time and it was time to pry the wallet open and just buy a new one. ;-).

Problem solved. I want to thank everyone for the information and guidance.

Here's what I did to solve the problem. I removed the IAC and cleaned it with carb cleaner. Reinstalled it and took the vehicle for a test drive. The moaning stopped at low RPM but now it was moaning at 2500 rpm. I knew at that point I was dealing directly with the problem. Next day went to the Ford service department and purchased the IAC for 129.00. I astutely asked the dealer if the part included the gasket, *remember to purchase a new gasket*, he looked in his system and found that it requires a new gasket, $2.00.

I went back to work, parked in the parking structure and replaced the IAC in less that 10 minutes. Problem solved.

I did notice that the IAC I removed did not have a gasket on it. I'm wondering if some service department mechanics don't know that the gasket needs to be replaced. The plastic footing for the IAC looks like a gasket, but isn't. I think the moaning was being caused by an air leak coupled with dirt and grime getting into the original IAC.

Anyway, everything is working fine.

Thanks again for all of your help.