As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED ENG ROUGHNESS. GROUND RUNS WERE MIXED, SOMETIMES IT WOULD RUN FINE. TROUBLESHOOTING LED TO INTERMITTENT GROUNDING AT KEY SWITCH. KEY SWITCH REPLACED. KEY SWITCH BACK WAS REMOVED. KEY SWITCH WAS INTERMITTENTLY GROUNDING INTERNALLY.