Chevy high RPM's

Hello: Well sounds like an air leak, or throttle plate not closing all the way. If the throttle plate (butterfly) is not closing all the way it will idle fast. If the IAC (idle Air Control) is not operating properly or carboned up not allowing the IAC valve to close far enough could cause fast idle. A leaking gasket under the throttle body assy (TBI) if you have one could cause it. Almost any air leak into the intake manifold could cause this. Possibly a rubber cavuum hose has split open or fell off somewhere.
Good luck
Darryl.

It sounds like it might just simply be your throttle positioning sensor. Fairly inexpensive to replace and any service staion with a diagnostic computer will pinpoint that right away.