If you remove the air cleaner and towards the back of the throttle body there is a fast idle valve. It is spring loaded. when it fails it will cause a high idle. Either the micro switch on the side failed or the valve itself failed. You can push straight down on the valve while the engine is running and see if the RPMs drop. There have been post about people shimming the valve to make it work. Also could be the coolant temp sensor at the front right of the intake.