That troubleshooting board is the best one I have seen yet. Where can you get that board at? Is it a polaris dealer tool? In all seriousness that is what I feel like most of the time you go thru everything I know and it still does it.
I think if you add some more details, peeps could offer more suggestions. Is this low altitude? high? 'tween?
Ever check fuel pressure? Maybe slap a gauge on and drive around. It'll at least be entertaining. what's the fp on the "good" sled in your group?
You said you had it to a dealer - what codes did you have? any TPS or throttle switch related?
What outside temps does the burble happen? after restarts? how long does it last?
what are the snow conditions when the burble happens? hard, deep, blower, flour, cascade concrete?
Is it just a different exhaust sound or does the engine lay down when this happens?
What mods do you have?
You've done all the right things so far - keeping a short log might help prevent doing something over. I worked on FI stuff for a lot of years and unless it was a weird japanese or english or french electronic glitch, a methodical approach usually solved the issue. That, and a thorough grilling of the customer. There is usually a clue or two that a customer reveals that helps in diagnosis. Since you are the tech and the customer, that exchange should be easy.
Lastly, since you have a good sled in your group, you may want to go through a step by step parts swap with that one until you discover what the issue is. You just have to convince your bud to help out for a half a day so don't do it on an epic snow day. YMMV.
