Having the same idle issue on my X5 N55, but I don't have a DP installed... Every once in a while it fluxuates up and down (with and without tune installed this happens). I don't think it's a tune issue, nor is it a DP issue... But strange that it only occurs on a few cars, and not every N55 car...
I've never stalled out though... Didn't pay much attention to the issue as In the X world, no one's complained about it, but since you guys are, thought I chime in that I experience the same.
BMW X5 35i: Boopie Exhaust, Boopie Intercooler, K&N Drop in Filter...
Audi S5 2013 (Delivery Sept 2013): Mods pending review