When you are cranking the car, is the check engine light illuminated?
It should be on as the engine is cranking or the ME control module has no power supply or is bad.
These cars were common to have one of the connectors on the k40 relay to come off ever so slightly.
This or a k40 relay that is bad could cause that problem.
Mercedes Benz Master Tech
ASE Master Technician
Owner of "Behind the Star Inc."