Thats not really how idle is set, that positions the throttle blades so iac count has enough.left to recover when you put it in and out of gear but a low enough iac # to NOT go to zero warmed up and idle too high. If this is a new problem (this uncontrolled high idle) and it was fine at one point, if you start pissing with that when problems actually a vacuum leak you will need to chsnge it back or iac will have no control once you fix actual problem, Smitty

OK.......I'll leave as is and search for what seems to be the main culprit a "vacuum leak"......is just a consequence that both engines have (at the same time) a vacuum leak?.......kinda weird to me, but we will eventually find it.

No it doesn't mean both have a vacuum leak. The high idle motor likely does or the throttle blades/linkage are not working correctly. Fix this engine/problem first, THEN we can address the other motor that stumbles.

Your original post said it was the port engine with the high idle???

It appears you have tall deck intake adapter plates, definitely look for vacuum leak!

just under the throttle bracket in the upper plenum there is a port in the side is it blocked off ?? this is where the hose to the lower center plenum ( PCV ) connects.

It is the port engine with the excessive high idle. The stb. engine (at idle) is barely running. feedback (I assumed) was vacuum leak, bad IAC or TPS for both engines.

Yes intake adapter plate, a bad seal there?

Winterized boat yesterday, but still have access.............whether blocked off or not, engines ran great until this season & considering no one touched anything before this problem I think it's a mute point.
Unless PVC has gone bad or hose detached.....but being blocked off ?...wouldn't that be an international move?