Riding Tractor engine reving fast after running into a stump

I have an Ariens 42 in ride mower with 17.5 BS engine.  It has been running fine that is until yesterday when I didn't see the remains of an old low cut stump while mowing some tall grass.
When I hit the stump I immediately shut off the engine (or maybe it shut off itself) pulled the tractor away and inspected the underbelly to find no hungup wood pieces and the blades looked intact.
The mower started up easily but the engine idled so high that it scared me so I immediately shut it off.  After looking over again, I restarted it and again same high rev-ing engine at idle that I shut it off again. I then rolled it back onto my trailer where it rests.
Can anyone suggest what the problem might be/ how I might approach fixing it.