As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT CREW NOTICED ROUGHNESS IN LEFT ENGINE. INSPECTED MAGS, COMPRESSION TESTED CYLINDERS, CHECKED SPARK PLUGS. ENGINE WAS GROUND RUN. FLIGHT OK'D. NOTED NO PROBLEMS. RETURNED TO SERVICE. NOTED: MINUS 21 DEGREES FAHRENHEIT TEMPERATURE.