What was found
WHILE DESCENDING INTO THE BASE AIRPORT, THE NR 2 ENGINE WOULD NOT ROLL BACK TO IDLE WHEN THE THROTTLE WAS CLOSED. THE THROTTLE APPEARED TO HAVE NO AUTHORITY OVER THE ENGINE AT THAT POINT. A SLOW ACCELERATION OF THE NR 2 ENGINE FORCED THE CREW TO SHUT IT DOWN. REPAIR STATION WAS CALLED AND ACCESSED THE PROBLEM. THEY DECIDED TO R & R FCU. AFTER THE FCU WAS R & R, A RUN-UP OF THE ENGINE VERIFIED THAT THE FCU WAS THE PROBLEM. ACFT WAS RETURNED TO SERVICE.