As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOTS REPORTED THE ENGINE WOULD RANDOMLY LOSE 50 - 200 RPM DURING CRUISE FLIGHT. REPEATED INSPECTIONS COULD FIND NO MECHANICAL BASIS FOR THE REPORTED ISSUE. FINALLY, WHEN THE ENGINE WAS GROUND RUN WITH THE COWLINGS OFF, AN OBSEERVER POSTED BY THE AIRCRAFT SAW THE THROTTLE CABLE END WIRE FLEXING AND TWISTING, CAUSING UNCOMMANDED MOVEMENT OF THE THROTTLE VALVE. THE TROTTLE CABLE WAS REPLACED.