As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED INTERMITTENT LOSS OF POWER ALONG WITH ENGINE RUNNING ROUGH. CHECKED EXHAUST VALVE GUIDE CLEARANCE IAW SB-388C AND FOUND 1 EXHAUST VALVE GUIDE WITH .002 CLEARANCE. (THE MINIMUM IS .015) REAMED THE GUIDE, ALONG WITH 3 OTHERS THAT WERE BELOW LIMITS FOR SERVICE AND RETURNED TO SERVICE.