Was the body replaced for this fault or rough running? The stepper motor is the usual fault but the grub screw that the motor acts on comes fitted to the body at max adjustment. You need to undo the allen screw out, this in turn tells the ecu its at idle. If you havent replaced the motor then try undoing the screw first and see if it makes a difference if not then the motor will have o be replaced.
Matt
October 2007