As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NOTICED WHILE DESCENDING THROUGH 5,000 FEET, THE MP WAS INCREASING AND NOT RESPONDING TO THROTTLE BACK. MP REMAINED AT 28 INCHES TO AIRPORT WITH THROTTLE SETTING AT IDLE. SHUTOFF ENGINE AND LANDED. FOUND THE NUT THAT HOLDS THE THROTTLE CONTROL ARM TO AIR/FUEL MIXTURE DEVICE WAS LOOSE AND THE SPLINES WERE SLIPPING. ENGINE IS SPRING LOADED SO TO STAY AT PARTIAL POWER IN CASE THIS HAPPENS. MINE FOR SOME REASON WENT TO FULL POWER.