My wife's 2007 E-320 Bluetec (V6) with 200,000 miles presently runs just fine, but won't pass inspection because of a CEL: P0101 (Mass Air Flow Sensors). I don't think it caused the problem, but it's worth noting that about 5,000 miles ago I replaced both air filters.

I was loathe to buy the $650 batwing with the integral MAF sensors, because I was skeptical that the MAF sensors were really bad. The car runs great. We routinely average over 35 mpg in Southern California stop and go traffic. I took a chance and cleaned the MAF sensors. I swapped the placement of the sensors when I re-installed them, hoping that I might figure out if one or other was faulty. That only made things worse--now the car ran sluggish. I can't say whether I ruined the MAF sensors when cleaning them (I used CRC MAF cleanser), or perhaps swapping positions screwed up the computer calculations. I bought two "new, OEM" sensors from E-bay. (They didn't appear either "new" or "OEM," but that's neither here nor there.) After playing musical MAF sensors, I can now get the car to run fine, but only with one MAF disconnected. (I have a "new, OEM" sensor in the passenger side, and the driver side is disconnected.) I have tried all the other three MAF sensors hooked up, and the car loses performance within about 10 miles with all of them. Immediately upon disconnecting the offending sensor, performance returns. Moving the "new, good" MAF sensor from one side to the other proves that the fault follows the other three sensors. I have a hard time believing three sensors are all bad (two old ones would have had to fail at roughly the same time--maybe even when I blasted them with MAF cleaner--and one of my "new, OEM" sensors must have arrived faulty). But, that's what the "tests" seem to show.

I read that sometimes a misbehaving EGR valve can cause P0101, so I cleaned it again. I had done it as preventative maintenance ~50,000 miles ago. I didn't notice any performance difference then, and I didn't notice any improvement this time, either.

I have only a generic OBD-II scanner. It claims to be erasing the codes. For good measure, I have disconnected the battery now three times (each time for more than ten minutes). I can't be sure that I have cleared all the faults, but I certainly have tried. I guess it's time to invest in a MB-specific scanner.

Is there something else I should be considering?

TL/DR: even with Check Engine Light illuminated (P0101), the car runs fine, but only when one MAF sensor is disconnected. My primary concern is passing inspection. What else might it be besides the MAF sensors??

 

The solution was to buy a Foxwell scanner and perform the "Reset values for HFM Drift Compensation" function.

The Autel MD 806 Pro was unable to perform that reset.

Anybody who needs access to a Foxwell scanner in Southern California need only send me a message. Thanks.

 

I have the same problem with my 2008 Blue Tec. It runs great with the driver's side MAF Sensor disconnected.

 

You need to reset the values for HFM Drift Compensation. I can do it for you if you are in Southern California. Your independent shop ought to be able to do it for, at most, a ~30-minute labor charge. Some PepBoys used to have professional scanners that they'd loan out (not the consumer-grade junk that AutoZone and O'Reilly's will loan you).

I bet if you look around Facebook or Reddit or MB World you'll find a Mercedes enthusiast who lives near you and who has a capable scanner. I see the Foxwell NT530 (which is the one I have) is $169 on Amazon. You didn't get the suggestion from me, but I bet that Amazon scanner has a 30 day window to return it for a full refund.