Originally Posted by Flatland2D
It'll rev from 1000 to 1500rpm once it reaches operating temperature. It'll usually die off sometime later, but sometime it'll go on forever. When first first starting up it'll rev up to about 2000rpm and drop to 1500rpm, where it'll stay until it reaches temp.
this honestly sounds like a "Fast Idle Thermo Valve" issue. I had this exact same thing about a year ago and is fairly common across all Hondas.