I get this code from time to time. The diesel engine codes are different than the gasser codes, I don't think it's fuel related - if you search this forum you'll probably come across my posts about this code, the P0120, and P0400 as well. In the diesel, these three codes point to something in the intake manifold, either the manifold flaps, the pressure sensor mounted on the bulkhead in front of the driver, or the EGR. You could have a vacuum leak in one of the hoses or vacuum switches, or in the vacuum actuator of the EGR or flaps. In any case, when the code is thrown, the ECU goes into a limp mode and mileage drops - mine usually drops to 25-26 mpg from a steady 27-28 in the city.

Look for vacuum leaks - my system shows about 20 inches of Hg of vacuum when it's running well. If you want more information, you can take it into a garage with the Mercedes specific machine and they will see more codes.

After 5 years of ownership my '97 has been very good overall with the exception of the complicated intake/vacuum system - this by far has given me more trouble than anything else.

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Charlie

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'66 VW 1300 96K miles
'97 E300D 239K miles
'85 300D 203K miles (sold Sep 2012)