I had the same problem, slow return to idle when hot. If you look at the plate where the throttle cable is mounted you will see a small hole on the bottom. Now look directly below to the engine and you will see a 1/4x20 Allen head screw. Get a "soft" throttle return spring, cut to length and remove the Allen head screw and drill a 1/16" hole in it and install the spring. Really easy as pie solution to the slow throttle return.
Mine does the same when hot. My understanding was that this was a deliberate ECU controlled feature to reduce emissions that tend to occur on throttle release. Hence it happens more when hot. But if there is a solution, hbatts, then maybe I'm wrong.
