Have had mine go high idle and i just removed the IAC cleaned it really good and put back on it did the job,Does not take much to make it stick couple grains of sand can do it from what i have seen.
Also had it go from idle to fast to slow constant like a light switch was also very rich and came out of no where when i reinstalled engine.That one turned out to be a bad coolant temp sensor.I used an ohm meter to test it,read it cold then used a lighter to heat the sensor see if it changed had nothing went got another one installed and everything was good.Had i not had a obd port i probably still be lost i was thinking it was a fuel problem at the time like regulator or injectors
