As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED "LEFT ENGINE RUNNING ROUGH AND WON'T IDLE BELOW 500 RPM". UPON INSPECTION MAINTENANCE FOUND THE NR 5 CYLINDER WAS READING ZERO COMPRESSION DUE TO AN EXHAUST VALVE CRACKED IN HALF. MAINTENANCE REPLACED THE CYLINDER AND PISTON ASSEMBLY WITH NO FURTHER DEFECTS NOTED.