Get a good flashlight, pull the air filter housing off, crack the throttle wide open, and have a look down inside the manifold. See oil pooling in there? That's a blown plenum. I expect *some* crud on the bottom, from the PCV system... but, pooling oil is a bad sign.

IAC is just a controlled vacuum leak. Unplugging the valve really doesn't change anything. Now, if you rev the engine with it unplugged, chances are good it'll stall when you let off.

 

thank you I’ll try that see what I see. As always I appreciate you exsplaining it so even a crayon eating Marine can understand