What RPM does your 2005 SP500HO Idle at?
It's supposed to be 1100 + or - 200 rpm. There is an idle adjustment screw next to the left plastic panel after you pull it. You have to turn that up (clockwise).
However, at the same time you have to make sure that the throttle cable adjustment is correct. It's about 4 inches down from the thumb throttle. You have to spread the rubber boot to reveal the screw.
If you have too little play in the thumb throttle then the quad will stall because of the electronic cut off. You want to adjust it for ~1/16" play. The idle need to be corrected too. You have to play with both to get it right. You don't want to just adjust one. Adjust both.
After you do all this give us a report.
If you have any questions, ask now.
By the way, in weather below 70 degrees mine idles like crap. I have narrowed it down to the pilot jet needing adjustment. Too bad the government required Polaris to put a brass plug over the screw so you can't adjust it. Next time I'll get the EFI.