We have 2 2006 Sportsman 500 EFI machines both purchased at the same time. Lately one of them has been missing randomly. Well after draining all the gas thinking it may have been caused by bad gas, changing batteries and trying everything I could think of, I found the problem and have fixed it. It appears to be a Air flow sensor on top of the throttle body that has 3 wires going to it. The wires did not have any wireloom or anything on them and was laying against the throttle body, one wire was actually worn through the copper and was randomly making contact. Resoldering the wire back together and wireloom and all is well. So then I look at the other machine and sure enough the wires were all but worn through. So I wireloomed them and hope not to have the same problem again. I'm posting this just so others can be aware of a potential problem and avoid the hassle later. Oh our machines have about 1600 miles on them of trail miles.

 

That is the T-BAP sensor(I think)
Theres a recall on it also.