A B767-200 IN CRUISE AT FL370 DECLARED AN EMER AND DIVERTED DUE TO LOSS OF L ENG CTL. CAUSE UNKNOWN.

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AT CRUISE AT FL370; ATC ASKED FOR A REDUCED AIRSPD. WE RETARDED THROTTLES (AUTOTHROTTLES ON) TO COMPLY. AFTER REDUCING AIRSPD; THE THROTTLES ADVANCED TO MAINTAIN SPD. THE R ENG ACCELERATED NORMALLY; THE L ENG REMAINED AT IDLE EPR EVEN THOUGH THE THROTTLE ITSELF ADVANCED ALONG WITH THE R THROTTLE. THE AUTOTHROTTLES DISCONNECTED. WE BEGAN A DSCNT AND CONTACTED DISPATCH AND MAINT CTLR. THE L ENG WAS UNRESPONSIVE TO THROTTLE MOVEMENT. WE TURNED ON ENG ANTI-ICE BUT THAT WAS NO HELP. MAINT CTLR COULD NOT OFFER ANY REMEDIES; SO WE DECLARED AN EMER THROUGH DISPATCH AND LANDED UNEVENTFULLY. CABIN ADVISORY ONLY WAS GIVEN TO THE FLT ATTENDANTS. MAINT WAS DEBRIEFED AND A LOSS OF THRUST RPT WAS SUBMITTED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED NO INFO ON THE CORRECTIVE ACTION TAKEN BY MAINT WAS AVAILABLE. THE RPTR SAID PRIOR TO DEPARTING FROM THE DIVERSION STATION; TWO IDEAS WERE TOSSED AROUND; BOTH SPECULATION. ONE; THE ELECTRONIC ENG CTL FAILED AND SECOND; THE FUEL FILTER ICED UP CAUSED BY THE FAILURE OF THE AUTO FUEL HEAT SYS. THE RPTR STATED MAINT HAS A POOR RECORD OF RPTING MAINT FAULTS TO FLT CREWS.