Paul, the line in question is a single line running from the intake manifold directly to the ICM. Remove the air cleaner housing and you will see the line in its entirety. It's actually a vacuum retard set up, i.e, the spark timing is retarded at idle when the vacuum is high, and advances as the vacuum decreases with throttle opening. A broken vacuum line would leave your timing permanently advanced = premature ignition, aka knock.
If your ICM is dud, these people http://4mercedes.com/index.htm rebuild them at a substantially lower cost than new. Dealers want about $3000 for a new one, other sources $2000. I got a working used one for $50 from these folks
austrianautoparts@yahoo.com. They might have others.
Good luck.