car,merc R129 2001 3.2L,now at garage with no throttle response but stops on idle prob.mechanic says message is being sent from potentiometer to ECU but cant tell wether its sending message to throttle body or faults with ECU.put a throttle body on that he had at home and made no diff but cant be sure it was working anyway.so its replace throttle body for £450 ish or ECU £1200or if make wrong choice both ,,thoughts anyone.