When Good Planes Go Bad

So I get to the airfield this morning and preflight N757MK.  Ok preflight except the oil is quite dark. Ray says today will be the day to polish up my landings and the weather couldn't be better.

I do a start up and the engine while it catches immediately is not sounding right at all. Throttle to idle turns the engine off unless throttle reapplied immediately. We take it to the run up and things start to get weirder.

Applying carb heat results in an increase of 500 rpm! This is really not right. Oil pressure is in the red and any setting throttle to idle results in the engine shutting down. Carb heat keeps giving weird increases.

We terminate and take it back to the flight school and it will not shut down - mixture all the way out and it still runs, fuel flow to off and it still runs, prop at idle and it still runs. Finally off with the ignition key. This is really not good as that's a hot prop situation waiting to bite someone.

Ray taxied it to maintenance and that was that.