cone filter on 2.0

I just got a rental for couple of weeks, it's a 2.0 2001 jetta GLS and got the idea of puting a cone filter on it sitting in my garage . Now as i was putting it in there there is a tube going to the airbox with no sensor ??? i left that tube just sitting there for now, is it bad for the car ? do i need a filter for that tube or not.