Those are the exact symptoms I had with the CPSU.

Has the weather been very warm or hot? Does the engine quit only during the day, but not at night? When the car was running great, was the weather cooler?

It could be something else (coil or ignition control unit) but it sounds like CPSU or some other heat-sensitive electrical issue.

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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