What is the vacuum part on the air cleaner lid?

Take a look at this diagram below. I suspect you are talking about the hose from the air filter housing to the oil fill cap or valve cover?

If that is the case, then this is part of the PCV system.

Basically, it takes fresh air from the air filter housing and the negative pressure (vacuum) from the intake manifold pulls any crankcase vapor out of the crankcase and puts in back in the engine.

If this is not the hose that you are talking about, can you get a picture of what you are looking at so that we can get on the same page?

If you think you have any leaks with this, we need to check for vacuum leaks.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please run through all this info and let us know what you find. Thanks