I should add:

You are not experiencing a complete buring of fuel by running lean. You are simply burning too little fuel to cause enough bad emissions to fail the test.

The test measures the net volume of CO/NO/HC produced, not relative percentages of fuel burned to "dirty" emmissions. Your emmissions problem, if there is one, will still be present, but of a lesser magnitude.

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black