What was found
PILOT REPORTED LT ENGINE PARAMETERS DIFFERENT THAN RT ENGINE, PARTICULARLY DESCRIBED AS LT FUEL FLOW DOWN TO 1250 LBS, HP DROP, LP DROP, AND HP VIBRATION WENT UP WITH THROTTLE MOVEMENT NOTED BETWEEN 0.48 AS HIGH AS 0.51 (THIS VIBE STILL WITHIN TOLERANCE/LIMIT). THIS WAS ANOMALY NOTICED AT FL450, MACH 0.83, AND OAT -63. THERE WERE NO EICAS MESSAGES POSTED AT THAT TIME. AIRCRAFT TURNED BACK TO DEPARTURE. DEFECT ISOLATED TO NR 2 ELECTRONIC ENGINE CONTROL (EEC) BASED ON ANALYSIS BY MANUFACTURER. DEFECTIVE UNIT REPLACED BY A REPAIRED UNIT.