could be an intake leak!! my exploder did this in the winter when it was cold! wouldn't run unless you held the gas down a bit and would run fine once it warmed up! took it to my cousins garage he did a test on it and turned out to be a leaking intake gasket! that's all i can come up with! I'm sure others will have more ideas! good luck! James
See the "Surging Idle Checklist for help with all your idle/stall problems. The first two posts contain all the updates to the fixes. I continue to update it as more people post fixes or ask questions.