HELP! 1991 yamaha 9.9 won't idle/low speed!

I've had this boat for almost three months (16' aluminum valco), and the 9.9 kicker has worked without missing a beat. Today, after having to use the kicker at full throttle for a bit when the big motor wouldn't go (low oil reservoir alarm..Oops!), later in the day, I had a heck of a time getting the kicker to start. It started cold and ran at the warm-up speed for a bit, then when the choke kicked off it died. It will run at higher rpms fine, but if you try to run it at idle or a low trolling rpm, it dies. <br /><p><br />I fiddled around with it a bit, and found that If I disconnected two vacuum lines coming from the manifold through what looks like a thermo-vacuum switch, then it would run with no throttle, but at a higher speed, then after I put it all back together again, it ran fine at a normal idle and low speed for about 2 minutes or so, then reverted back to dying.<br /><p><br />Another couple of things: I didn't let it warm up much when I first put it to use today, since I needed power and was drifting in an ebb tide along the edges of the shipping lanes. And when I first was running it, a few drops of oil came out the crankcase vent by the water outlet. I checked the oil and it seems very overfull, although I have used this motor quite a bit over the last two months wihout a hitch, and the guy had just changed oil when he sold it to me.<br /><p><br />Whew! So I need this thing to get up and running by next tuesday or so, any ideas? <br /><br />Thanks a bunch in advance,<br /><br />Mark