Thanks again for sticking with me on this all!

Late last year I checked base timing which for some reason seems was grossly out of adjustment as detailed in the above post.

Why would such a large adjustment be necessary if the hold down bolt was incredibly tight?

Nonetheless, the boat ran good on the water but still had one instance of off idle rpm surge; however, the usual stall on hose at the ramp (hot engine) while trying to flush was prevalent. As usual the rpm's had to be brought up to 1200 for it to run on hose. As a reminder if I shut the boat off on the water and restart I've NEVER had the issue I do on the hose when hot.

At a complete loss other than checking compression; however, my vacuum reading (lowest 15 hg) doesn't demonstrate weak compression.

Keith

When you checked timing was the motor placed in base timing mode?

Yes sir.

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

See post #2......

Would I not be seeing a drop in vac gauge pressure between hot and cold or less than spec? I do not.

I've searched for leaks all up around the plenum and intake mani areas. Nothing can be heard and carb cleaner spraying in said areas netted nothing but paint removal.

No, the ac stays the same, the change comes from the temp sender once it reaches operating temp, then the ECM reduces fuel

I don't know, just seems like that's all there is. It may be leaking under the intake, drawing from the engine block. Again, I don't know and have run out of ideas

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??

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.

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

Chris