What was found
CREW REPORTED, 55 MIN INTO FLIGHT, DURING CRUISE AT FL350, NR1 ENGINE (ENG FUEL) ANNUNCIATOR ILLUMINATED. LIGHT EXTINGUISHED WHEN POWER REDUCED BELOW 90 PERCENT N1. REQUIRED FURTHER POWER REDUCTIONS TO FLIGHT IDLE TO KEEP LIGHT EXTINGUISHED. DIVERTED FLIGHT, DISCREPANCY VERIFIED AT ARRIVAL. REPLACED ENG FUEL FILTER AND PERFORMED PRECAUTIONARY DRAINING OF WING FUEL TANK SUMPS. NO REPEAT OF FAULT AFTER 45 MINUTES OF EXTENDED GROUND RUNNING AT VARIOUS POWER SETTINGS. REMOVED FILTER RETURNED TO MAINT FACILITY FOR FURTHER DETAILED INSP. (K)