914UL dies at idle / rough idle

What rpm are you idling at?

Hi Alex

They type 914 has a turbo so carb ice is almost impossible because the incoming air is heated by the compression of the inlet air.  (It heats it up) Given the temperatures it may be lean burn due to the denser air you are in.  I would try to set the needles one notch richer before anything else.  As for fuel mogas is unlikely to make a difference vs avgas relative to idle.  If you have a set of EGT on the engine it may give you a better indication of rich or lean burn as well. 

Also consider if the engine has been sitting for a while that you may have varnish in the float bowl on the float pins or in the low speed jet.  It may be worth taking them off and checking that also.

Cheers