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Weird (loud) harmonic noise from engine


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11 replies to this topic

#1 eryque

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Posted 04 August 2007 - 03:26 PM

This doesn't seem to be my day. After monkeying around with things for a few hours I decided to go run some errands. Now the engine produces this weird harmonic noise that sounds like low frequency feedback in a PA system.

It's not the fans, I checked that. The noise is present as long as the engine is turning and stops when the engine stops moving.

Here's what I did today:

- Removed MAF housing from intake, sprayed it with MAF cleaner (didn't touch the sensor), and reinstalled it.

- Removed intake air box, cleaned throttle body, replaced box.

- Installed new horn.

- Drilled a hole in a heat shield and inserted a sheet metal screw to keep it from rattling. (Something is still rattling, don't know if it's that one or not.)

Any ideas? I don't think anything I did would cause this, but the noise wasn't present before. I don't like weird noises.

#2 porcupine73

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Posted 04 August 2007 - 03:37 PM

Are you sure all the hoses on the bottom of the intake tubing is reconnected? There are a number of hoses down there that come off somewhat easily if messing with the air filter or maf, plus they're on the bottom of the intake tube so it's not immediately noticeable if one came off.

#3 eryque

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Posted 04 August 2007 - 06:34 PM

The noise is coming from this hose, which looks like it connects to the bottom of the throttle body. It's a weird harmoinic noise like something's vibrating or rubbing, the same sort of note you get when you rub a wet finger around a wine glass.

I sprayed throttle body cleaner in there and scrubbed it out. That doesn't seem like it could be causing this, does it?

Posted Image

#4 porcupine73

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Posted 04 August 2007 - 06:39 PM

I'm not completely sure but I think that might be your idle air control valve (IACV) intake hose. Is there anything down inside there? If not, i'd get 'er idling and give some shots of throttle body cleaner down that hose with engine running. There was a note on EndWrench about certain vehicles making a whistling noise if the iacv is dirty.

#5 eryque

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Posted 04 August 2007 - 06:43 PM

Well, when I plug it with my thumb (at idle, butterfly closed) the engine dies, so I'm guessing this is the idle air control hose.

I'll try it out.

#6 porcupine73

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Posted 04 August 2007 - 07:06 PM

Ok. You could also pull the hose off the other end in your pic right at the iacv. You still hear this noise even when that hose is connected to the intake tubing? I mean so that the air going into the iacv is coming from after the air filter?

#7 eryque

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Posted 04 August 2007 - 07:18 PM

I did take off that hose, and yes, the noise is still there.

I used a mirror to take a picture down in there, does this look real gunky?

Posted Image

I made a video so you can hear the noise. When I put the hose back on the noise is pointed right at the camera so it really sticks out. I took it on and off a couple of times so you can hear the difference. The noise I'm worried about is the consistent, unwavering harmonic sound. The chattering doesn't concern me much right now.

http://www.youtube.com/v/JY1JkbmUn0A

#8 porcupine73

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Posted 04 August 2007 - 07:32 PM

It looks a little carbony in there. Did you try spraying throttle body cleaner in there with the engine running at idle? Like a short burst so the engine sputters a little but doesn't stall, and repeat at least a dozen times.

#9 eryque

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Posted 04 August 2007 - 07:48 PM

I just did a couple of squirts. It worried me a bit when the engine sputtered, so I stopped.

Off I go...

#10 porcupine73

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Posted 04 August 2007 - 07:54 PM

It sputters because although the throttle body cleaner is flammable, the engine doesn't get enough air with it to run properly, so it sputters. Nothing to worry about really.

If you already gave it a few squirts and it's still doing it, then I either wouldn't worry about it or you may need to take the iacv off to examine it (but beware it has a gasket that needs to be replaced if you remove it). Some chunk of dirt or a flake of something might've gotten down in there and is acting like a whistle or reed for a musical instrument.

#11 eryque

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Posted 04 August 2007 - 08:08 PM

That sounds like a job for Next Weekend Man.

Is it as complicated to remove as it looks at first glance, or is it just because there's a bunch of hoses and wires and stuff?

#12 porcupine73

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Posted 04 August 2007 - 08:12 PM

I haven't ever had to remove one; the throttle body cleaner spray in the intake there is all I've ever needed to do. If you do decide to remove it, make sure you get a new gasket first.

Another idea might be to get a shop vac down in near that hole and see if it'll suck out any particles or chips. I'm guessing, that if it wasn't making this noise before work was started, and it is making noise now, that something might've gotten down in there.




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