What was found
REACHING FL390, AFTER LEVEL OFF, LEFT ENGINE EXPERIENCED TWO SEPARATE THRUST REDUCTIONS WITH ACCOMPANYING AIRCRAFT VIBRATIONS. AFTER EACH SEPARATE REDUCTION & VIBRATION, THE ENGINE RECOVERED NORMAL OPS. NO LIMIT EXCEEDED AND MC NOTIFIED. COMPLETED QRH PROCEDURE FOR ENGINE LIMIT, SURGE, & STALL. REMOVED AND REPLACED THE FUEL CONTROL AND PERFORMED ENGINE RUN, NO LEAKS AND OPS CHECK NORMAL IAW AMM 73-21. REPLACED EEC PT2/TT2 PROBE IAW AMM 73-21. AND PERFORMED HIGH POWER RUN, OPS CHECKED NORMAL.