I really think it is this. Merc should have more idle air thru the blades and little thru iac. Big propped boats with little engine torque at idle will need mire isc action, but......

I wonder if opening the tb blade up a touch to lower the iac percent would make the iac last longer? (Draw less amps). I know BUP (am I allowed to say that? Lol) would say it has to be a certain percent (20 or 30٪ if I remember right) for a warmed up engine at idle.

When I tune my cars I usually set the desired idle rpm about 50rpms lower with the iac disconnected.

Yup, but your tps had to be within spec still as that will move. If not, and If tps is adjustable, and/or you can program your computer to your idle setting spec.

We are on the same exact page.

Merc could/should do better on this issue for sure. Especially since these issues have been going on for so many years now across mist all motor lines.