What was found
DURING CLIMBOUT, THE NR 3 ENGINE N1, N2 AND NR 3 EPR BECAME ERRATIC, ALL OTHER INDICATIONS NORMAL. CREW FOLLOWED COCKPIT OPERATING PROCEDURES AND RETURNED TO DTW WITHOUT FURTHER INCIDENT. REPLACED THE N1 AND N2 INDICATORS. ALSO, REPLACED THE NR 3 N2 TACH GENERATOR, PERFORMED NR 3 ENGINE RUNUP AT FULL POWER AND NOTED N2 STILL FLUCTUATING. N2 WAS MEL'D AND AIRCRAFT RETURNED TO SERVICE.