Modern Vespa

07 GTS 250 with 44k miles, runs great but sometimes I get 4 bars opposed to 3 bars normally on the RPM screen. The scoot is trying to move forward. This only happens after 10 miles or more, when cold, the idle is normal.

FWIW, I have the same issue sometimes when the engine is cold and the weather cooler. I've found that giving the engine a little rev will sometimes make it return to normal rpm's. More often just killing and restarting the engine will do the trick. And the golden cure-all has been to ride it to temp, shut down, restart and then it's been good to go.

You MIGHT have a failing, fouled, or disconnected air temperature sensor on the throttle body, which isn't detecting the cooler air, so it's letting too much dense air in, creating a slightly lean mixture, which can cause idle speed to be too high. If you're looking for a little project, get to the throttle body and spray some throttle body cleaner around and see if that helps. Can't hurt.

It does sound like a sticky throttle plate to me. I had a carbed tractor that did the same thing.