Hey I was having similar problems with my 91 300E, it seemed to be something in the Idle control circut. But on yours it might be the injectors??
I replaced mine to no avail..
I replaced my cap and rotor, deffinately needed, but no differece.
I replaced the EHA, it was leaking, no difference.
I replaced the OVP, no change, but more about this later.
I pulled of the idle conrol valve and ran 7 volts through it to check and make sure it was working, and reinstalled it.
ONLY then did the car start acting right.
I don't know if it was the combination of a new OVP and testing the ICV or what...
I put the old OVP back in (it rattles) and it does not make a difference, so hard to say.
It has been suggested that the "Potentiometer" might have been a problem, but I don't think it was in my case.