That is your vent line which does go into the passenger compartment so it has "clean air"

http://www.ultrahot.com/vacuum/egr_82_300d.jpg

look at the injection pump and then for the black/white line that goes to "a".


So we need to look other places for your problem.
Start by buying a Mityvac unit. Then lets figure out if you have good vacuum or just a leak. With the Mity vac you can start the process of eliminating components on your system that could be causing the leak.
Quickly you can diconnect and BLOCK ( a golf "T" works well) the door lock and AC system vacuum lines.
The door locks are the Yellow/red yellow/green lines. The Ac system are the Greeen lines. The brown lines are the shut off lines that go to the Injector Pump. Try the door and Ac lines first. Isolate them and see if the car shuts off. If it does NOT then we need the Mityvac to start at the vacuum pump and work our way thru the system.

If the car is old and the 2/3/4 way rubber connectors have not been replaced they do get old and cause leaks.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car