just as a word of warning.. technically, you aren't supposed to clean IAC's... carb cleaner being the weapon of choice usually due to the carbon buld-up... it's supposed to be a strictly replace part...
they can be cleaned, and gotten to work again most times, but they are often known to fail pretty quickly after said cleaning..
I have seen both occasions... cleaned and held up fine, and cleaned and fubar'd in short order..
obviously it could be other issues, from a vac leak to a stuck throttle, but with TBI's, the most often issue I've ever found with high idle, is failed/stuck IAC's.... unlike a dry mpfi manifold, the TBI's tend to crud them up...
99 out of a 100 of these issues I find in the boats, are IAC's.. I probably replace a dozen a yr at least usually... whereas, I've probably replaced 1 to 2 TPS's (other symptoms obviously) in the last 5 yr's.. it's a VERY common failure in my line of work.. they get crudded up, hang up and stick... in your case, water may have free'd up some crud, lodging in the seat.. or maybe a bit of rust if some time elapsed...
