As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) PILOT RETURNING TO BASE NOTICED RAPID TORQUE GAUGE FLUCTUATION BETWEEN 5 PERCENT TO 10 PERCENT, OCCURRING MOSTLY AT AROUND 85 PERCENT TORQUE. LATER PILOT AND AME CONDUCTING TEST FLIGHT TO CONFIRM PROBLEM NOTICED SLIGHT ENGINE SURGING NOTICEABLE ONLY BY ENGINE SOUND, NO OTHER GAUGES INDICATED ANY PROBLEM. AFTER EXTENSIVE TROUBLESHOOTING, IT WAS FOUND THAT THE FUEL CONTROL UNIT WAS CAUSING THE TORQUE FLUCTUATION.