I have been tracking down a rough idle on my 190E 2.6 recently. Many lessons learned! I would suggest looking at the rotor and cap for corrosion and general wear, check the resistance of the tips on the spark plug wires (I found a bad tip among other things), and check out the Electro-Hydraulic Actuator (mine was leaking around the gasket and may be worn out). And in the end, probably some roughness is to be expected with idle + A/C. Hope this helps and that Benzmac will be recovering away from work, leaving Steve to correct me!
89 190E 2.6
83 300TD Turbo