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What Mike said!
The density is the key for the ME fuel injection computer to determine the amount of fuel is required to optimize the ratio. That is why your car can run like crap when the AMM is going south, as the fuel mixture may be incorrect.
Measuring air density that quickly and accurately has been a challenge for most makes, and the AMM is not an uncommon failure on many OBD-II compliant cars.
Talking to a tech, he figured the cycling of the AMM was responsible for less wear than the damage to the "strand" caused by the abuse of teeny particles slamming into it. He explained that it gets "pitted" and the increase in surface air erodes it's accuracy. Larger particles can wreck it altogether. Now, I don't know the validity of this, but he has lots of happy customers that get very high mileages out of their AMMs by changing engine air filters frequently and only using OE filters in OE housings. He had a new customer come in with an ML that had an old air filter and the AMM housing was filled with gunk and so was the downstream intake plumbing. The AMM was shot.
Now, I didn't start out seven years ago on the C230 changing my air filter often to save the AMM. Heck, I had no idea of what one WAS! But, after years of changing the filters often (along with frequent oil/filter changes) and my engines still in top form at 400,000km's or more, I figured I must be doing something right. It works. Our 190E 2.6 is just about to roll over 400K (250K-miles) and the head has never been off, the tranny is original (serviced often) and the car runs like a top.
As to the fellow with the C230 with 175K-miles, perhaps he could take the time (appreciated by the many C230 owners around) to give us some insights into his C230. Tranny problems? Any mileage related difficulties? I know a fellow with a 96 C220 with about 410,000kms and he's had some AC problems (replaced a couple condensors) and a few small complaints, but otherwise he's had over 250K-miles of trouble free motoring.
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