As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE ON CLIMB OUT AT 2500 RPM AND 25 INCHES, ENGINE RPM SUDDENLY WENT TO 3000 AND PILOT WAS UNABLE HAVE ANY EFFECT WITH PROPELLER CONTROL. AIRCRAFT RETURNED TO AIRPORT USING THROTTLE TO CONTROL RPM. ENGINE CONTROLS WERE ALL FOUND TO BE INTACT AND OPERATING NORMAL. UNIT REMOVED AND SENT TO PROP SHOP FOR REPAIR.