The mass air sensor is located in the big, fat plastic tube that is located between the box that holds your air filter and the intake manifold.
It is held in by simple hose clamps, and takes 10 minutes to replace.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".