hmm i dont remember right now, its been on loan to a friend for a while. but i remember that it idled just fine. have you tried adjusting the idle speed up a little bit? the homelite i have just has carb mixture adjustment screws on it, try leaning or richening the screws a lil bit to see if that smooths it out. does the BX90 have a trigger throttle or is it like mine where it just has choke and run which are selectable by a lever? vibration could also be caused by a broken impeller blade. check in the blower casing to make sure none of the blades are broken.