Loud vibrating hum coming from air box occasionally

[sdowney717]

I put my hand on the airbox when it makes this horn like sound and it is vibrating hard.
I found some info pointing to an IAC and throttle body dirty issue.
Our car is a 1998 Ford Contour with 2.5L V6 engine.
It will randomly start this loud humming horn noise, and it may go away when revving the engine.
Has anyone ever experienced such a thing?
I have been wrenching a few decades, and this is a first for me.
I thought it was the electric rad fan, so replaced that, then I thought maybe idler pully bearings, but I jumped out and checked when it was making the loud hum, and found it is the airbox top.
I then opened the airbox like to look at the filter, and the top kept vibrating.
The vibration is intense, there is no mistaking it.
It is definitely coming out of the intake manifold.

Thoughts?
It is a weird problem.
Sounds like a car horn at a low level.

This guy had the same problem on a truck engine.
https://www.ford-trucks.com/forums/1690199-2002-f250-5-4l-loud-humming-noise.html

 

[JohnnyG]

Probably resonation. Some intakes are designed with large blind tubes that go nowhere, just to combat this issue. I'd check to see if similar cars of different years made any changes to the intake tubing and go from there.

 

[sdowney717]

Probably resonation. Some intakes are designed with large blind tubes that go nowhere, just to combat this issue. I'd check to see if similar cars of different years made any changes to the intake tubing and go from there.

We have had the car in the family for 15 years, when my FIL died, wife got the car. It never did this till a few months ago.
It idles fine.

Maybe I should pull off the intake and or throttle body and clean them.

 

[Mechanician]

It's a good idea to clean the TB. Many times the idle will be different afterwards. Can't you clean the throttle body without removing it?

 

[Nukeman7]

Try this as a test: remove the air filter and see if that eliminates the humming noise. If it does, replace the air filter with a different brand. It could be creating resonance harmonics/oscillation due to air flow restriction from a dirty or densely restrictive filter. Or possibly due to the foam gasket hardening or shrinking, resulting in a poor air seal.

 

[sdowney717]

Try this as a test: remove the air filter and see if that eliminates the humming noise. If it does, replace the air filter with a different brand. It could be creating resonance harmonics/oscillation due to air flow restriction from a dirty or densely restrictive filter. Or possibly due to the foam gasket hardening or shrinking, resulting in a poor air seal.

I thought about it.
But as it was vibrating, I opened the air box and removed filter and it kept vibrating as I held the cover lifted up.
Filter looks clean

 

[sdowney717]

Now a month ago, wife was driving and car was accelerating by itself. She was parked, started, put into gear, engine revved and she hit a tree.
Another time I was in car and engine bucked for 10 seconds like speeding up and slowing down fast.

I thought maybe the IAC valve was sticking-bad, so I put in a new one, and all the odd revving went away.
What we don't know for sure is if this horn like noise started then or was still happening before replacing the IAC.

I still have the old IAC, and thought I could oil it and put it back in.

It is mostly driven by her, so my knowledge is more limited.

The noise to me is more of an annoying thing, but for her it makes her think it's going to break down on her.

It was shocking to feel how much of a strong vibration was coming from the air box cover. And the rubber bellows that connects to the throttle body. Yes, I can remove TB and try to clean and check all passages.

 

[Mechanician]

I have seen noisy IAC valves. You should be able to clean your old one well with TB cleaner.

 

[sdowney717]

Took a video of it humming.
You can hear the horn like sound.
Then at video end, I open air box and it get very loud, then ends after a few seconds.
I can 50 feet away hear this horn sound.
https://photos.app.goo.gl/UBz63BkxMrvkPDmv9

At 25 seconds is the new IAC valve, been on a few weeks.

 

[WobblyElvis]

When idling and making the noise, unplug the idle air control valve. See what happens. Clean the throttle body. Clean the outside of the air box and add some stick on wheel balancing weights to change the resonance of the box. Open the box remove filter and put in some large items that can't be ingested into the engine [ spray can cap?] With large hose clamp secure a heavy item to the side of the accordion intake tube.

 

[D60]

If cleaning doesn't work, I'd be curious what misfire counts are doing as it's idling.

 

[IndyIan]

Maybe there is a little resonator piece on the bottom of the air box that's fallen off?

 

[sdowney717]

If cleaning doesn't work, I'd be curious what misfire counts are doing as it's idling.

It is a very smooth running engine, idle is like you don't even know it is running.

 

[sdowney717]

I originally thought the noise was a failing electric cooling fan.
Well, to replace that, the radiator has to come out the bottom.
The fan is bolted to radiator
AC condenser can be unbolted from radiator and stay in there, flops around loose, you have to tie it up.
I put on a new fan, and it did not fix the noise.

In removing the radiator, after I put it together, the AC failed, it now has a leak, will not hold a full charge, compressor cycles and little cooling. I recharged and it cools great and it loses the charge within 5 minutes.

I scratched the condenser surface in a line about 6 inches long, but I spray water on it and dont see a leak.
It is a gouge that disrupted the aluminum plates though.

I had to lightly pry the suction line next to battery and it has a connection there to the drier bottle.
I was prying it out of the way to attach upper hose clamp to radiator.

And dropping the condenser down I see cracked hoses, outer rubber cover has checks, but it had those and never leaked.

Now I am stuck wondering what to do with the AC leak. Potentially 3 areas, the scratch, the drier connection, the hoses to condensor.

I can get a new condenser for $50.
Any thoughts on the most likely problem?

The system holds a pressure, it just does not hold a full charge.

 

[sdowney717]

Another hum thread on a Ford.

https://www.ford-trucks.com/forums/976335-loud-humming-coming-from-air-intake-3.html

Could it be the rubber hose bellows is worn and weak?
The outside of this is decayed, gets your fingers black, rubber is disitegrating.

 

[sdowney717]

I could scrub off all the disintegrating outer rubber. Then use SikaFlex 291 and coat on new rubber layers. And that will strengthen the hose. If it is too weak, the rubber bellows might be setting up a resonance effect, just like a horn.