Yes, the IP does auto-adjust for barometric pressure by moving the regulator along the rack at all throttle positions (not just at idle) when relative pressure is less than 1 atmosphere. That, and the way the cone in the IP is mapped (it is milled in three dimensions but it is not concentric: rather, it is parabolic shaped, and how MB decided how to do this is a mystery to me) is one of the most amazing engineering feats, perhaps one of the real engineers on the board can give a quick tour.
Best,
g
'64 230sl, fully sorted out...ooops, spoke too soon