[bmckay]

Next time it happens check the breather/air filter for moisture. It could be starving it for air. If not I would guess a short somewhere which goes away when it dries out. I dought it's the Idle air control valve itself. More likely it's being shorted out by the moisture. Usually sensors either work or don't, but not intermitently unless there's a bad connection or in your case moisture is shorting it out. Just my guess.