Hey Guys,

I have a 75 914 2.0 D-Jetronics Injection. Can anyone tell me what the two holes that run through the bottom of the Plenum are for? Seems to me this would be a vacuum leak?

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They are hollow internal support tubes (look inside the plenum). They don't all leak, but when they do its often at the interface with the outer shell of the air plenum. They can be soldered or sealed if they leak.

Look at the interior
I believe the holes are a pipe that is run all the way through and is sealed so as to not create a leak

Its a chamber on which significant vacuum is applied (when appropriately sealed) . Without some stiffening/support it would collapse / cave in.
The tubes provide that stiffening & to protect from the inevitable top pressure of installing the air cleaner.
As Jeff mentioned they crack around the brazed points

Thank you guys very much.