vacuum leak

[qwerty247]

I am trying to find a vacuum leak as i have a slight rough idle and can hear a hissing in the engine.

can anyone point out the most common ones to check ?

and when i pull a hose off what should happen to the engine?
if that the one leaking will it then run smooth?

just not sure what to be looking out for when i pull the hoses?

thanks for any advise !

[CanMan]

I spray carb cleaner around all the hoses, the TB and intake gaskets, and other places that take on vacuum. If the engine stumbles, you have found the source of the leak. HTH.

[Matthew Currie]

When you pull a hose, the leak will probably get worse, and the engine should speed up. It's possible that if your vacuum leak is bad enough, then pulling the leaky hose will have less effect than pulling a good one. You might also hear the hissing stop, but it will be hard to detect with the other noise. I'd test by either clamping off the lines near to the manifold (you can use a needlenose vise grips as a tubing clamp), or plugging the nipples on the manifold after removing the hose. If your leak is in a hose, then the problem should disappear when you block off the right one. If hoses don't work, look at the manifold gasket and the throttle body gasket. The carb cleaner trick is probably the best way to track that.

[qwerty247]

thanks for the info !

I pull each hose off and the engine speed up, however i think i found the hissing one and its the ccv one.

but could that hose be causing bad mpgs?