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Every since I installed my M-1 intake manifold and 14X4 round open air cleaner when I first start the truck I hear a loud hissing noise. Well earlier after I finished up fixing my vacuum lines I noticed that it sounds like it is coming from the front of the intake manifold under the breather. The air cleaner is sitting on the manifold good and tight and there is a gasket there. Is this just normal from the intake and air cleaner?
 

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it's the AIC valve letting air in to adjust the idle. Perfectly normal, noticed it also when I installed my chrome hat air intake.
You don't usually hear it with the stock box because it muffles the sounds so much.

It should quieted down once the engine warms up or you give it a little gas.

Mine's disconnected so I don't have any hiss :D:
 

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Mine does it too, with that ram air hood it sounds like a turbo under boost..

If it keeps doing it even after it's warm, and your idle has increased from normal it's normally the gasket under the TB, or a intake gasket to the head leaking by..

Choppy idle is a vaccum line, sometimes it may not be choppy and your idle will increase a little, but it's normally not loud enough to hear it unless you right up to it..
 
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