When I first bought the car I had no MB experience and I thought I could easily fix this "minor" problem by throwing a few parts at it, since everything appeared to be original, and the car was in great shape overall, mechanically (ie no oil burn or leaks, firm shifting auto trans and solid suspension).
The other parts I've change since I bought it (and made no difference) include the fuel pressure regulator and the EHA valve, both new. I'm strongly suspecting the fuel dist at this point, but am feeling a little humbled (and light in the pockets) from my previous attempts to solve the rough idle.
I must also mention that the car has been to the dealer in order to get it to pass smog, which it now does. Again, this made no difference in the idle/off line hesitation/sputtering.
I think I'll start taking a more linear/logical approach to figuring out this problem by checking things such as EHA current and duty cycle that I've seen being discuss in this forum. I'll post the results as they are found.