So I had my vacuum gauge installed in my 98 cav 2.4L just recently.  Having driving the car for years I just realized something.  My vaccum line was never connected.
How would this have affected my car and what difference should happen now that its connected??
 
having a vaccum leak would make the car idle rough
 
 
Also, that vacuum line could have been sucking in debrit and sending it directly to your throttle body.