Car: 2008 E350 4Matic Sport

When stopped in gear I can frequently feel vibrations. When I place my hand on the engine cover I can definitely feel it.

Observed Symptoms in past 6 to 12 months
* Cold starts can be sluggish -- by a second or two

* On occasion, on hot starts, after car has been idling then shut down and restarted a a few minutes later, the car will crank but not start on the first try but fires up solidly on the second. This happens only very infrequently (and actually sounds like a cam sensor issue).

Recent Work in Past 2 weeks:

* Engine mounts (today)
* New Spark Plugs
* New Engine Air Filters

Anyone else experience this?

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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