As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ACFT ON A TRAINING FLIGHT. A REPORT WAS MADE THAT THE ENGINE WAS RUNNING ROUGH AND IT FELT LIKE IT WAS RUNNING ON 3 CYLINDERS. DECLARED AN EMERGENCY, DIVERTED MADE AN UNEVENTFUL LANDING. AN INSPECTION PERFORMED BY MECHANICS VERIFIED A VALVE WAS STICKING INTERMITTENTLY. CYLINDER WAS REPLACEDT.