Mine started having a faster idle since this summer / fall. Initially it was around 1800-2200 & now it's that at startup & as soon as it's warm (very soon), it idles around 3000-3200. Years ago I had a leaking intake gasket & fixed it myself, but due to being low on coolant & using it to drag an 18' trailer w/ a couple of CL car finds on it back to my house (and getting it hot) - I suspect I lost the intake gasket again.

If I spray carb cleaner on the lower back right corner of the intake manifold, my idle actually slows down for as long as I spray. I haven't gotten around to replacing the gasket again yet, but doing this should confirm your issue.

Good luck!