The same exact thing happened to my 98 E320 with 58K last week. I ended up replacing the mass air flow meter for about $400 at a local shop. However, You can replace this part yourself very easily for less than $200 in less than 5 minutes. I would have done it if I had anyway of checking the code. I know that Autozone checks faults for free but there isn't one near where I live.

The problem can also be a faulty oxygen sensors which should be covered by 7 years or 70K emission warranty in California. Call your local dealer to see if your mass air flow meter is under the emission warranty.

S.