These have a little sensor in the power steering pipework (sometimes behind the front bumper, to the right, looks like a little metal cylinder screwed into the pipe at a 90 degree angle) with a beige plug (I believe) these are prone to the wires breaking, if this has happened, it can cause the high revving you describe. Also the ISCV (Idle Speed Control Valve) can cause it, clean it out with some carb cleaner and see if it helps.