I'm having a problem with the engine idling fast right at startup - up to 3000 rpm, and never goes down... the choke plate stays open, and bumping the throttle does nothing. Manually closing the choke plate takes the idle down but of course it won't stay that way. Does it just need cleaning, or does the problem seem more serious? i've been doing a little work on it since I purchased it a few weeks ago. It had a problem of missing while idling and sitting still while in gear, but I changed the plugs and wires and that seemed to help. any comments on how to fix the iding?