Problem in showing customized 404 error page

To show custom 404 error page I did the following

$route['404_override'] = 'errors';

where errors is my custom controller. Now above this is working if controller/method not found.But suppose if we passed some parameters after the method name them its not working and shoeing the default 404 page

For example: (domian name)/(controller)/(method)/(incorrect parameters) , it execute default 404 page rather then my custom 404 page

Is something I am missing ?