My rock isn't holding the vacuum it should, ~17" @ idle, and I am having a doosie of a time tracking down a leak. I have beaten the throttle body cleaner test to death, and capping off the different vacuum ports on the manifold one at a time did nothing. Is it possible to have a vacuum leak on the inside of the engine? Maybe on the wet side of the intake manifold/head gasket? Would this area of the engine, right where the push rods are, be under manifold vacuum becase of the PCV? Has anyone heard of a vacuum leak like this, or in any other unusual location?

Help :hail:

what is it reading at idle

brake booster can leak internally

It's reading an unsteady 17" at idle, like I mentioned above. I've heard people say it should be closer to 20" with a stock cammed tpi, but I can't seem to find a vacuum spec in any of my service manuals.

To eliminate the possibility of leaks in the various systems that use vacuum, ie. the brake booster, I disconnected them one at a time and capped off their source of vacuum while eyeing my gauge. I did this procedure for every vacuum lead I could find anywhere on the manifold. This would be the brake booster, FP regulator, the other bigger one by the FP reg. lead, the one under the TB, the one on the right of the TB, and the one for the PVC. None of this rasied the vacuum above 18".

Did I forget any vacuum leads?

Anybody have anything else, maybe concerning an internal leak like originaly mentioned?

I'm Clueless

I wouldn't be worried about 17 inches of vacuum, depending on your cam.

but even with a stock cam this could be fine.
how many miles?

but if its really unsteady you could have a miss, but then the needle on the gauge would boce around all over

It is possible to have a vac leak to the lifter valley, but You should see some evidence of Burning oil if this were the case.

17" at idle isnt anything to worry about, IMO.

I had oil on # 1,3,and 7 plugs and didn't have any external vacuum leaks and my driver's side intake manifold gasket was blown. That was 3 months ago and I have the same symptoms again but no oil on the plugs this time. My vacuum reading at idle is 16" and I never checked it when the problem was gone. I don't wanna tear down the TPI again.