The bad news: The propeller governor is the culprit and it will need to go out for overhaul. It wouldn't be so bad, but the governor is the hardest part to remove from a Mooney engine. It's at the base of the engine, right up against the firewall, which means the engine will need to be partially removed to get at it. Mr. wallet is not happy right now.
So I'm now grounded until we can get this fixed.