As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED LEFT ENG BETWEEN 16,000 AND FL220 ENGINE WILL ROLLBACK FROM 87.2 TO 85.9. THE ENGINE WILL ROLL UP AND DOWN TILL FL220 THEN IT STABILIZES. MX REMOVED AND REPLACED FUEL PUMP ASSY ON LEFT ENGINE WITH OPERATIONAL AND LEAK CHECKS GOOD. A/C WAS APPROVED FOR RETURN TO SERVICE.