What would cause this?
 

In my slingshot i can run the boat and pull the throttles back and star side engine will not go back to idle and rpm will read 2,000. Was thinking a cable was getting stuck but the only way i can get it to go back to idle is to turn that engine off and fire it back up. It's like something gets reset and if it was a throttle sticking i wouldnt think that turning the engine off and back on would make a difference....Its a 502 dynoed at 602 hp carbarrated...If anyone might know whats going on let me know id greatly apperciate it!

What kind of distributer? Could be weights/advance getting stuck. Once it stops spinning it will then go back. I do think there is something else besides that. Any special igntion box? It could also the carb throttle blades are sticking until the vacumm is gone then they will shut.

Yes its got msd ignition and distributer...