You are running the HSN too lean. When you do a WOT run, and then let off the throttle, the engine won't idle down right away as the mixture is still lean. With a correclty adjusted LSN, the idle will eventually die down to normal as the mixture richens up after a while.

Open the HSN up about 1/4 turn (rotate CCW)and see what happens.

Here's a video of a mild case of your trouble. The "High Speed Too Lean" banner starts around 0.55 seconds into the video. Start paying close attention around the 1:00 minute mark. Notice he drops the throttle around 1:07, the idle stays high, then it drops to a normal idle at 1:10

http://www.youtube.com/watch?v=BJFsJ...eature=related