I had a flight in a 300C with a recently replaced ("new") engine that had a few snags...
Flying along, ~1000' lowered to a cruise setting ~16" MAP IIRC when it started to flutter...
Amazing how quickly training kicked in selected a spot and entering auto.
While doing that instructor suggested rolling up throttle to see if that helped, which it did, reapplied power and returned to base.
Had an issue with valves on one of the cylinders and some mag issues.
What pleasantly surprised me was how natural my actions seemed entering into the auto, not rushed, and "in tune", inspite of how quickly it happened, even the ability to do diagnostics on the way down.