Welcome to the forum You are describing a typical crank position sensor failure. This is also known as a reference sensor. See below. Easy to replace.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1QF0V26SB1UL10X198&year=1998&make=MB&model=E-320-005&category=All&part=Reference+Sensor

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2012 E350 Bluetech