Welcome Luke. Not familiar with your motor, but until someone knowledgeable chimes in, the shaped air breather hose from the valve cover to air cleaner has a small tube that attaches on the other end to the fuel pressure regulator. That's not a vac line, but merely a return line in case the fuel pressure regulator diaphragm ruptures, it'll keep raw fuel from dumping onto hot engine surfaces. At least that's how the M103 works.

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't