As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) IN CRUISE AT 2,400 RPM THE ENGINE ABRUPTLY LOST 200 RPM AND BEGAN TO RUN VERY ROUGH. AFTER LANDING THE FAULT COULD NOT BE DUPLICATED. SUSPECT EXHAUST VALVE(S) STICKING INTERMITTENTLY. LYCOMING SERVICE BULLETIN 388B CARRIED OUT. ALL EXHAUST VALVE GUIDES WERE REAMED AND TAPPET CLEARANCES CHECKED WITHIN LIMITS. ENGINE REASSEMBLED AND EXTENSIVE GROUND RUN-UP CARRIED OUT. NO FAULT FOUND, AIRCRAFT RETURNED TO SERVICE.