I thought it would be helpful to put this in a separate thread. Some of you may have seen my parallel thread in which my M104 MAF is suspected to be faulty:
http://www.peachparts.com/shopforum/showthread.php?p=1543618#post1543618
In my research I stumbled upon this VERY HELPFUL document which outlines exactly how to test a MAF. No more guessing - it is a very exact procedure:
http://www.x-desk.net/ximages/21302_pgsi0079en.pdf
The output voltage of a healthy MAF is supposed to be around 1.00 plus or minus 02 with key on engine off. Upon starting the engine, it should rise to 1.6 and then travel all the way to between 3.8 and 4.4 at full throttle.
When I tested mine, the output voltage was 1.462 with key on engine off, which is way high. When I blew a little bit into the MAF, the voltage would go both up and down (it should only go up) and was very erratic. Upon starting the engine, it was at 1.64 (a tad bit high). I didn't bother with the full-throttle test, as it was very evident to me that the MAF was malfunctioning.
At least I think I know what's going on now. My E320 M104 is still driveable, you just can't accelerate slowly. Have to give it lots of throttle from a standstill or it will go flat. I will be ordering a new MAF as soon as I can.
Oh, and the document also settles the debate over whether or not there is actually a difference between the $130 MBZ element and the $59 generic (VW, Ford, Audi, etc.) element. Definitely different part numbers, so I wouldn't even mess with the generic since I like my catalytic converter the way it is.