I am fightin the same problem on my 560SEL and i have not found the problem yet. Some things to look at further that come to mind-
1)check the coolant sensor and the resistance values
2)check the EHA valve wiring and resistance (it should be about 19 ohms).
3)check the idle control valve wiring and resistance (should be about 5 ohms).
4)Check the OVP relay and fuse.
5)U should also check for fuel pressure leak down.
Good luck and hope u find it.keep us posted.
With mine the idle is very rough until the system goes into Lambda and then it smooths out and speeds up. If i restart immediately it starts right up. If i let the car sit for 45 mintues is starts hard again. Scratchin my head still.