View Slows Down When Selection Criteria is Used

We have a view that returns with results very fast when executed without any selection criteria

       select * from our_vw;

However, when we add the selection criteria it runs significantly slower; from a second or two to several minutes.

        select * from our_vw where cpsid = :B1;

Does anyone have an idea on why this is happening? 

We recently upgraded from 9i database to 11g database and have run an explain plan on the view's query and it all looks OK.  It us just when we try to use the view where the issue is occurring.

thanks

Alan