The IAC (Idle Air Control) in these are like an opposite bees wax coolant thermostat, closes up when the coolant flowing around it gets warm. It is the component on top of your throttle bodies with the 4 little screws in a square pattern that you see between the bracket for the headlight pod... Sounds like it's sticking internally and won't close, probably caught some grit or shavings in the coolant and bound up.
We had a wierd IAC failure last year on a FPP Turbo Attak where it closed up too much and wouldn't allow enough air by and gave us a wild goose chance because it produced a too rich condition, perceived to be a fueling problem and wasted a whole day of trouble shooting... Replaced the whole throttle body assy, so the IAC might not be available separate?