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Discussion Starter · #1 ·
I think I have a vacumn leak under the intake manifold. When I turn the idle adjustment screw to increase the idle speed, a hissing sound starts coming from under the manifold. The more I turn the screw, the louder the hissing gets. (I've checked all the vacumn lines against the diagram in my manual: they seem to be in the right places).

Is this normal? If not, any guesses as to what it is? I hope I don't have to take off the manifold again :(

Also, is it normal for the PCV valve to hiss slightly?

Thx in advance
 

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my PCV valve doesn't hiss... if you wiggle it around does it change in it's sound?

the vacuum leak you're talking about... are you sure it's not another type of leak (intake manifold gasket?) since you sound like you have just removed & replaced it...

did it just come out of nowhere or has it been there awhile?
 
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Discussion Starter · #3 ·
The 'leak' started after I replaced my VCG's & installed phelonic spacers: now the car idles a bit erraticly and stalls sometimes.

I'm pretty sure it isn't the intake manifold/head join. I used a plastic tube as a stethoscope: there is no hissing from the intake manifold/head join.

Using the plastic tube, the hissing seems loudest when it's inserted under the manifold, next to the plug wires.

I also replaced the PCV valve: maybe the new one is bad?
 
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Discussion Starter · #4 ·
Heck CountZero - I am having the same problem. I hear the same hissing sound coming from behind or under the engine. I had a vacuum hose hanging, which I plugged back in but the noise is still there. I suspect another hose loose somewhere. Keep me posted if you find out where your sound is coming from. If I find mine first I will let you know.
 

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There's one hose I had a problem with when I did my rear VCG install. It's the hose that attaches to the vacuum chambers (black boxes under the manifold). Let's hope it's not that; it's almost impossible to see with the manifold in situ.

Tyson
 

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mts3 said:
There's one hose I had a problem with when I did my rear VCG install. It's the hose that attaches to the vacuum chambers (black boxes under the manifold). Let's hope it's not that; it's almost impossible to see with the manifold in situ.

Tyson
What is the purpose of these vacuum chambers ?

I wondered bout it when i replaced the cam cover gasket on the rear.
 

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hmmm, same problem here ....
friend of mine when i had my hood opened noticed when i turned the engine off that there is a hissing comming somewhere around the iar intake. well we tried to locate it and its like comming somewhere from bellow the idle screw .... and my idle sometimes stays at 800 then it slowly gets up to like 1300 and then down again ....
anyway i didnt have it fixed yet so guys keep posting about that. once i know whats wrong with mine ill tel yall know. Martin
 

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Those two black vacuum chambers are just that - reservoirs that hold a "reserve" of vacuum to operate the various vacuum-controlled actuators like the VRIS during times when there is little manifold vacuum (such as at WOT).

A one-way check-valve (visible if you remove the #1 plug wire and look down near the plug well) ensures that the chambers always have enough vacuum, even at WOT.
 
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