What is this vacuum for?

I have a 2002 gmc yukon denali.

I bought and it had a cracked intake manifold. Well actually it was a small hole. Like someone tried to install audio system on it and accidentally made a hole on the intake.

It was plugged with a ear plug. I removed it and applied apoxy for a temporary fix. Well it turned out to be 2 years before I could get to it.
I bought a used intake online. In excellent condition.

Bought new gaskets and installed it about 3 weeks ago. Worked great.

My water pump went out and when I was checking where my water pump was leaking from I had the engine running and I could hear a vacuum leak and it was leaking from the upper intake. Like if a hose goes in there or something.

I tried to look for any loose hose but couldn't find any. Maybe the intake was for a different model?

you can always take it off and look up the part number be careful though brittle plastic

compare it to the old intake? other wise you will need to get a cap for it

That one on my '04's intake is plugged.