As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AS POWER WAS REDUCED FOR DESCENT, THE LEFT ENGINE POWER LEVER WOULD NOT RETARD FROM CURRENT POSITION. CREW CONTINUTED TO DESCEND AND AT FL200 THE POWER LEVER BEGAN TO FUNCTION NORMALLY. AIRCRAFT LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE FOUND FIRE RETARDANT MATERIAL OBSTRUCTING LEFT ENGINE CONTROL CABLE PULLEY. MATERIAL WAS REMOVED, OPERATIONAL CHECK OK.