my fuel mileage after the first 300 miles is 20 mpg mixed 50% highway 50% city and I think it is doing OK.

As to the engine being loud, it is subjective and compared to my 1996 E320 which I find a bit more quiet with almost same odometer stand (169K).

About PPI and emission I think like you that it is not recognizable.

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1996 E320 since 1/16/08, 171K miles as of Feb 2011

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1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE