What was found
(CAN) DURING CRUISE AT FL105, THE ENGINE POWER ROLLED BACK ALL THE WAY TO IDLE. THE PILOT TRIED CYCLING THE POWER LEVER TO NO AVAIL. THE EMERGENCY POWER LEVER WAS USED TO RECOVER ENGINE POWER AND THE ACFT RETURNED TO THE DEPARTURE POINT WHERE AN UNEVENTFUL LANDING WAS MADE. POST FLIGHT BORESCOPE FOUND NO ENGINE DAMAGE. TROUBLESHOOTING LED TO THE REPLACEMENT OF THE FUEL CONTROL UNIT, FCU, BEFORE THE ACFT WAS RETURNED TO SERVICE.