So, I went looking for the Alda after reading thread after thread about it (including just removing it along with the pollution stuff).

It looks to me like on my '87 300D it's inconveniently located under the intake manifold. The light was fading and it was chilly out so I was eyeballing the sender screwed into the manifold. I took it out and cleaned it with carb cleaner and started up. I thought it started a little better but I can't swear to it.

Then I looked at a thing near the turbo that looked like an Alda to me.
The single pipe on it goes behind the air cleaner and when I tried to trace the other end it popped up from behind the air cleaner "box" with a split rubber sleeve on it. Clearly a coupling of sorts.

I started up and felt a slight vacuum on it so I stuck a golf tee in the end and went for a short drive. It felt stronger to me.

Forgive my simplistic experiment, but what is that thing and am I doing any harm by plugging that line until I can sort out where it's supposed to go?

Thanks

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Albany, NY Suburbs
'87 300D