As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ENGINE RUN-UP, PILOT REPORTED EXCESSIVE RPM DROP OF RT MAGNETO AND ALSO NO VACUUM. AN INVESTIGATION REVEALED THE REAR MAGNETO BEARING FROZE AND THE IMPULSE COUPLING BROKE OFF AND DESTROYED DRIVE GEAR THAT RUNS THE VACUUM PUMP AND THE REAR ACCESSORY CASE WAS CRACKED. OUTSIDE AIR TEMP WAS MINUS 28 DEGREES CELCIUS AND FURTHER INVESTIGATION FOUND THE TANNIS ENGINE HEATER WAS NOT PLUGGED IN.