The european 190E has got a valve in the vent opening that can be (manually) closed and opened. If air is still floating through this vent when it is closed, the valve does not close entirely.
If you take a look through the vent grating, you can see an "imbus"bolt that is attached to the valve that can be closed. This bolt has to be tightened to let the valve close entirely; the valve can be "fine tuned" by this bolt...
with a minor 600+k