If the throttle shaft is worn, bushings can help and possibly help the high idle. As the engine is running, wiggle the shaft and see if that makes a difference. I fixed mine with a sliver of brass sheet bought from a hobby store. You can usually get them in as assortment pack. I took the throttle plate (butterfly) off and removed the shaft and wrapped the brass around the shaft and worked it back into position. With trial and error you can find the right size.