As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE PILOT REPORTED A ROUGH ENGINE IN FLIGHT AND RETURNED TO AIRPORT, A SAFE LANDING WAS MADE. MAINTENANCE GROUND RUN AIRCRAFT AND A FLUCTUATION IN FUEL FLOW WAS NOTED. THEY FOUND THAT THE MIXTURE CONTROL WAS STIFF WHEN MOVING, (POSSIBLE GALLING).