2001 Mercury Cougar IDLE

ORIGINALLY MY CAR WAS DYING WHILE IDLING AT STOPS BUT OK WHEN IN PARK (WITHOUT A LOAD ON IT)...I HAD FRIEND MECHANIC TAP WITH A HAMMER ON THE IDLE AIR CONTROL VALVE AND IT SEEMED TO FIX IT FOR A FEW DAYS...i HAVE REPLACED THE IDLE AIR CONTROL VAVLE AND IT DOES NOT DIE OUT AT STOPS WHILE IDLING BUT IS STILL JUMPING AND NOW THE ENGINE LIGHT IS ON?

DO THESE SYMPTONS POINT TO SOMETHING IN PARTICULAR....INTERIOR LIGHTS SEEM TO BE AFFECTED BY THIS JUMPING IDLING....DOES THIS TELL ME IT IS ELECTRICAL IN NATURE?

IS IT FUEL RELATED (PUMP OR INJECTORS)
WILL A TUNE UP POSSIBLY CURE THESE THINGS

THANKS FOR YOUR TIME
BILLY