[Dave at Pelican Parts]

Two main things could cause a high idle.
1 - more air going into the intake
2 - ignition timing over-advanced

For 2, check your timing. Dig out a timing light and our Tech Article on the procedure and have at it.

For 1, the first thing to do is look for hoses that have fallen off. This seems like the most likely cause of a very sudden air leak. Next, try moving the throttle valve and see if it does close smoothly.

--DD