There is a throttle play adjustment at the bottom side of the throttle tube mount. Loosen the jam nut and turn the adjust out until you have 1/4" of free play. Don't forget to snug-up the jam nut when you are done.

I adjust my cable so that I can feel just a tiny bit of free play when the throttle is closed.  Just a tiny bit of movement of the wrist before the cable starts to move.

Check to be sure that you can move the handlebars fully right and left without the cable being pulled and changing the idle speed.