Originally Posted by zz28zz

You can check for internal vac leak by plugging all the holes in the valve covers except 1 where you press down with with the palm of your hand to seal the last hole with eng idling (cold eng is waay more comfortable). If you can feel that suction is building on your palm, you have a internal vac leak like suggested above.

On a side note: I once "upgraded" all the intake manifold bolts on a SBC car eng. Didn't realize the new ones were slightly longer. They would tighten down just enough to start compressing the gaskets then bottom out. Replaced the gaskets twice before I figured out what was going on. It had a internal vac leak.

Anyway, its a quick and easy thing to check for.

What's was the deal with the stripped intake plenum bolts mentioned on post #90? Could that be a potential vac leak??

Originally Posted by Trash

It could be a hairline crack some where in the intake manifold 'hat' or the surrounding gasket. As the motor warms up the expansion can cause a larger air leak. Just a thought.

Originally Posted by Blueabyss

Rent one of those smoke machines and do the smoke test.

Chris

Originally Posted by Tractionless

UPDATE

I had the boat on the water last weekend in cooler than normal weather. It seems as a result I only had one stall issue after a rev and it did not die on the hose when flushing at the ramp. Would ambient temp. affect a vacuum leak?

Thanks

Originally Posted by AllDodge

Not seeing a difference with air temp, but the MAP could effect the fuel supply

Originally Posted by AllDodge

With my pea brain it has to be vacuum leak because

If vac line is removed, fuel pressure increases
IAC is trying to idle but is not rich enough but is when cold

Originally Posted by articfriends

So aside from a weird ghostmechanical problem (I doubt) , the only thing you HAVEN'T tried is swapping the harnesses side to side? IF you hadn't bought mefi scan and saw 64 degees C for ECT Id suspect the ect or wires but no way it would read what it does, that's my only suggestion reading thru this as you asked, Smitty

Originally Posted by Tractionless

Thank you for your time!

I haven't swapped harnesses but it's worth a try or maybe I can try one of those self contained testers that takes the place of the harness. The name escapes me at the moment.

Keith