When speaking about the 1981 to 1985 5-cylinder turbodiesel engine:

"...there is a black line coming off the bottom of the vacuum control valve and going into the firewall.  This is a "vent to passenger compartment" line and is not connected to anything under the dash."

According to Kent Bergsma's "Vacuum System Troubleshooting" Mercedes Diesel Repair Booklet;more info @ http://www.mercedessource.com

- Fred

'82 M-B 240D 211K * '86 Porsche 944 turbo 54K * '70 Triumph Bonneville 650 *