What was found
(CAN) THE NR 2 ENGINE IS ACCELERATING UNCOMMANDED WHEN THE TORQUE IS GREATER THAN 50 PERCENT. THE ACFT RECENTLY DID AN AIR RETURN DUE TO A SLOW TORQUE FLUCTUATION ON NR 2 ENGINE. THIS FAULT APPEARS TO HAVE BEEN RECTIFIED BY REPLACEMENT OF THE HMU. THE SUBSEQUENT GROUND RUNS APPEARED NORMAL UNTIL THE POWER LEVERS ARE PUSHED ABOVE 50-60 PERCENT TORQUE AND AT THIS TIME THE NR 2 ENGINE STARTS AN UNCOMMANDED ACCELERATION THAT REQUIRES THE POWER LEVER TO BE RETARDED. TROUBLESHOOTING IS ON GOING.