# A (probably) dumb question about the Valve cover to airbox hose & PCV setup



## Jettaboy1884 (Jan 20, 2004)

Hi,

I've had several CIS cars over the years, but I never really noticed this before:

The hose that goes from the valve cover bung to the airbox is the PCV breather, correct? And that port on the airbox is filtered air, but not yet metered, right? But, I see that from that same bung on the valve cover, a hose goes over to one of the two large bungs on the intake manifold plenum.

So, how is this not allowing unmetered air to get sucked into the intake, bypassing the throttle body? Or is it, and that's intentional?

Pic of Vac system for reference:


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## Butcher (Jan 31, 2001)

Unmetered air is air that bypasses the airflow meter. So, assuming you are correct and the hose [that is not pictured] goes to where you are saying, yes, it's unmetered. 

Not all air is metered, the brake booster is not, as well as the purge air from the carbon canister, and don't forget all the vacuum leaks a typical CIS system has.


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