Thanks, JeffC and Jonny, for your advice. It was very helpful.
The whole emission control system has been very confusing to me. I looked into the MB Service Manual, and it shows emission control system for a carburetted engine and nothing for injected engine, and fails to note that they are different. Compounding the confusion is my own car where emission control has been tampered with by the previous owner. The vacuum lines to the two-way valve are disconnected, relays and their mounting bases missing. I am trying to figure them out to be able to restore my car to its original working condition.
I have two vacuum ports on the intake manifold. One of them should be connected to the two-way valve. The other one, I assume, is a test port, which needs to be kept capped. Is that correct?
Regards,