What was found
AIRCRAFT WAS GROUNDED: DURING CRUISE, DESCENT, APPROACH, AND TAXI IN, LEFT ENGINE FUEL FLOW WAS SURGING APPROX 200 POUNDS PLUS + AND MINUS. VISIBLE ON ENGINE PARAMETERS N2, N1, EGT, ALSO FELT ON THE AIR PRESSURE IN THE CABIN. TAXI IN FUEL FLOW ON RIGHT ENGINE WAS APPROX 600 POUNDS LEFT ENGINE WAS VARYING UP TO 890 WITH ALL EQUAL THRUST SETTINGS. REPLACED LEFT ENGINE PRESSURE REGULATOR VALVE PER AMM 36-11-52 (AALA202102229002) AND THE THERMOSTAT SOLENOID PER AMM 36-11-43 (AALA202102229021). A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED.