High/erratic idle and white smoke - 350 EFI

I've been having occasionally high idle speeds (1,100 rpm) for the past few weeks, normally if I shut the engine off and restart it goes back to normal.

Today the idle was all over the place and kicking out more white smoke than I'd like while surfing. It smelt pretty gassy too. The boat is running fine, other than the idle issue and white smoke. The White smoke seemed intermittent, some surf pulls it would smoke and others it was normal. The boat is also surging a while in gear to pick up a rider.

On the way back the dock, the boat ran great at cruising speed and I opened it up for a few seconds with no problems, no smoke either. It's a 10 minute ride to the marina, and the idle seemed to be back to normal once we got there.

Any thoughts? Air Idle Control, coolant temp sensor, or too much ethanol in the gas?

The engine is Merc Magnum 350 EFI.

I just took a closer look. My hydrophase speed control linkage on the throttle body had come loose and was literally hanging by a thread. I tightened it all up and readjusted. I also cleaned the IAC as well. We'll see what happens.