As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MOMENTARY ENGINE ROUGHNESS/VIBRATION/LOSS OF POWER. ENGINE FLUCTUATING 200-250 RPMS AT ALL RPM SETTINGS ON THE RAMP, DURING TAXI, AND DURING THE RUNUP. RAN THE ENGINE ROUGHNESS CHECKLIST WITH NO CHANGE. UNABLE TO GET A FIRM READING ON THE MAG DROP DURING RUNUP DUE TO FLUCTUATIONS SO WE RAN THE FOULED SPARK PLUG CHECKLIST WITH NO CHANGE.FUEL SERVO REPLACED.