I have the same problem on my 300E...it's intermittent now, but at one point this year, I went ahead and took the plunge and replaced the MAF...no change whatsoever after the replacement.
I had bought the part from Performance Products (my pre-forum days), and fortunately, they had a no-questions-asked refund policy.
I have yet to find the cause, but I DO know that it is not the MAF...look elsewhere.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car