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Tea kettle under the hood

TRevs

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I noticed a whistling noise a few weeks ago. It seems to be coming from the area around the throttle body.

Hopefully the noise is audible in the video, which I’ll try to post in a few minutes.

Supplemental info:

- I do not hear it at all in the first few minutes after a cold start, but it appears once the engine gets to operating temperature.

- it’s subtly present at idle, but any minimal pressure on the throttle makes it louder, even if the throttle isn’t moved enough to raise the RPM. It seems to go away when the throttle is opened enough to rev the engine (although it may simply be drowned out by engine noise).

- I replaced the throttle body gasket a few weeks ago. Used a Fel-Pro, and tried to be careful about cleaning the mating surfaces without scratching them.
 

rasband

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I replaced the throttle body gasket a few weeks ago. Used a Fel-Pro, and tried to be careful about cleaning the mating surfaces without scratching them.
If it's new since this change, that would be my first guess. You could pop off the air intake just to rule that out and selectively feel around the various vacuum lines going into the engine.
 

freedom_in_4low

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I had something similar resulting from a crack in the intake hose upstream of the throttle body. It was on a fresh rebuild and started screaming at me on my first drive, about a mile or two from home.
 

freedom_in_4low

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If it's new since this change, that would be my first guess. You could pop off the air intake just to rule that out and selectively feel around the various vacuum lines going into the engine.

I agree that it's probably related... My hunch is that it's not necessarily the gasket but something that was disturbed during that work, and a decent chance it disappears with the intake disconnected.

Don't forget to check the pcv hoses and fittings, too. I cracked one once just pulling the intake hose off the TB.
 
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TRevs

TRevs

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If it's new since this change, that would be my first guess. You could pop off the air intake just to rule that out and selectively feel around the various vacuum lines going into the engine.
you can feel a vacuum leak with your fingertips? I thought it would take a smoke machine or something.
 
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TRevs

TRevs

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... and a decent chance it disappears with the intake disconnected.
So run the engine with the plastic intake hose disconnected from the throttle body?

and if the noise goes away with it disconnected it proves the hard plastic intake is the source?
 

freedom_in_4low

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So run the engine with the plastic intake hose disconnected from the throttle body?

and if the noise goes away with it disconnected it proves the hard plastic intake is the source?

Yes.

And yes or something connected to it. The pcv system has a hose running from the main intake pipe (or air box, depending on the year) to the valve cover.
 
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TRevs

TRevs

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I'm disappointed. I was expecting a new mod to go with the muffler pot.
1649764035544.jpeg
 

TJ Jim

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Mine had very similar sounds that you explained. I replaced the exhaust/intake gasket to solve mine. A bit embarrassing. I’d stop at a red light and shed whistle quite the tune. It was a bit intermittent.
 
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TRevs

TRevs

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Update:

I ran the engine with the intake hose disconnected and the whistling didn't go away. In fact it seemed louder. I checked all the other vacuum lines and the connections/hoses seem good.

I remembered that when I replaced the throttle body gasket, I also removed the TB itself and cleaned it. It wasn't that dirty, but I wonder if I damaged the plate or something. Are those things fragile? It's not an electronic/servo drive-by-wire throttle like everything else these days, so I wasn't too worried about manipulating it.

Might have to remove the TB again and inspect carefully.
 
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TRevs

TRevs

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Update #2:

The whistle is still present; it only happens when the engine has warmed up; it is moderately loud at idle, and gets noticeably louder with the slightest pressure on the throttle cable (not even enough throttle to increase RPM), then goes away when the throttle opens enough to raise the engine RPM.

I’ve cleaned the IAC with the Jerry Bransford method mentioned in other threads, sprayed water around every vacuum line, and removed the throttle body again to clean and re-seat the gasket and bolts. None of that has changed the whistle.

I removed the IAC from the TB and sprayed it out with TB cleaner. No help.


It seems clear that the whistle is coming from inside the TB itself. With the air intake tube off amd engine at idle, I can reduce/eliminate the whistle by blocking air flow at the “6o’clock” position of the throttle plate. There’s a fair bit of air moving between the plate and the wall of the TB at idle. The wall and the plate in that area look smooth and clean.

Is there supposed to be air leaking around the edge of the plate at idle?

Did I damage the throttle plate by cleaning it? Is the spring weak and not closing the plate?
 

Gollywomper

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Spray some carb cleaner around the base of the throttle body. Engine rpm will change when sprayed on the leak. My guess is there was a piece of old gasket or something causing the leak.
 
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TRevs

TRevs

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A cheap stethoscope would probably help you find where the noise was coming from.

I used a mechanic stethoscope with everything assembled and couldn’t localize the noise any more than the throttle body itself. I’ve searched and sprayed for leaks but I’m convinced there are no leaks from the outside.

I found the source of the whistle on the interior of the throttle body; the noise goes away if I disrupt or block air that is seeping through the bottom of the plate.

I can try to take a video to illustrate. I’m just wondering if I caused the throttle plate to be out of alignment somehow with my original cleaning, so it doesn’t seal properly against the side of the TB at idle.
 

Shawn rube

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I used a mechanic stethoscope with everything assembled and couldn’t localize the noise any more than the throttle body itself. I’ve searched and sprayed for leaks but I’m convinced there are no leaks from the outside.

I found the source of the whistle on the interior of the throttle body; the noise goes away if I disrupt or block air that is seeping through the bottom of the plate.

I can try to take a video to illustrate. I’m just wondering if I caused the throttle plate to be out of alignment somehow with my original cleaning, so it doesn’t seal properly against the side of the TB at idle.

I am interested to if you found it. I’m having same issues. please help it’s driving me crazy
first jeep an it’s pissing me off.