SJS i would 1 clean inside the throttle body with carb and intake cleaner spray.Remove the air filter you will see a flap inside the throttle body gently push it down as you spray in the cleaner. It will get rid of all the old black crud that might stop the flap from closing. Do you know anything about the potentiometer ,this little thing is fixed to the throttle body ,in side its a carbon track this wears out as the metal rubbs it like a radio switch.Might be worth a check .