possible vacuum leak, but no boost leak?

[Devilsfutbol17]

When my car is idling I can hear a loud hissing sound from the top of my intake manifold. It sounds the loudest when my ear is right over the word "multi" on the manifold. My idle is occasionally rough and will surge sometimes. I am doing boost leak tests up to 20 psi but I can't find one single leak on the manifold. I'm about to check/adjust my base timing in an hour or so though to see if that's my problem. I idle at about 16inhg. This is on my GVR4. Thanks.

 

[onefast2gdsm]

I think it should idle at 18inhg, that's what my gst idles at.

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[burningforce]

A leak is a leak spray some engine/brake cleaner around that area and see if the idle changes.

 

[LiquidX]

Did you use a spray bottle of soapy water for your boost leak test? Not all leaks are audible.

 

[Devilsfutbol17]

Thank you for your replies. I have sprayed everywhere with carb cleaner and couldn't find a leak any where, it was idling smooth. I soaked the top of my manifold with soap and water and didn't see anything. I previously had a major leak on the throttle body shaft, but I just recently replaced the shaft seals and its not leaking any more. I just can't find the large hissing on the manifold.

 

[LiquidX]

Did you check your injector seals and vacuum lines back there? Don't forget about the brake booster line.

 

[Devilsfutbol17]

I did end up finding a major injector seal leak after testing again very cautiously. Im away in college and I just got home and just replaced the seals that go to the head and the o-rings on the top of the injectors. I started the car up and the hissing doesn't sound as bad, but I can still hear it. I will have to wait until Sunday when I go back to my fiance's place to do another boost leak test. I did see a minor increase in my vacuum though.

Also my timing appeared to be way off, atleast thats what it looked like for the first ten seconds before the timing light decided to quit working. So Ill be grabbing a new light and checking the timing again on Sunday as well.

Thanks for the help, I will update Sunday as to what the situation is.