As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED ENGINE WOULD FEEL LIKE IT WAS GETTING A MISS IN FLIGHT. PERFORMED A RESISTANCE CHECK OF THE PLUGS AND FOUND HALF OF THEM TO BE AT LEAST 10 TIMES OVER THE SERVICE LIMIT RESISTANCE VALUES FOR THE SAME PN FOR A TEMPEST PLUG. THE ENTIRE SET OF SPARK PLUGS WERE R & R WITH TEMPEST OF THE SAME PN AND THE PROBLEM WAS CORRECTED.