Guys my MC18 has trouble on idling, not as if it dies on idle but it idles at about 4000 RPM.

just to clarify the problem... Upon starting the engine it will run ok and idles at about 1500 RPM. but when I rode it for a while and stop, put it in neutral and lets it idle, it rises at 4000 rpm.. it feels like sometings stuck or what... it sometimes happen and sometimes not...

anyone have an idea on how to fix it?