I wish I could help with your actual problem, but I cannot. I can, however, commiserate with your statement above. Despite its relative dependability over 14+ years of ownership, my wife's 2006 E350 wagon has been consistently underwhelming. People post glowing reviews on Diesel Discussion of the w211 CDIs. But I always feel like it's not the engine on my 2006 I dislike (the engine has actually been rock-solid and returns great gas mileage); instead, I feel like the rest of the car is the problem. It's finicky, difficult to dial in, and even when everything is working 100%, it feels just....blah. I'd rather drive my 35 year old diesels (and that's not really intended to be a compliment to them).

Anyway, I hope someone has a constructive solution to your problem.

__________________
Christopher
'06 Mercedes E350 station wagon (silver/black)
'85 Mercedes 300D (black pearl/palomino)
'85 Mercedes 300SD (smoke silver/burgundy)
'79 Cadillac Sedan DeVille

'05 Toyota Camry (because always running is nice)

'85 Mercedes 300D sold back to orig. owner 8-1-06
'84 Volvo 264GL Diesel, owned 2000-2013