Code Igniter: Routing to controller/method/id

Code Igniter: Routing to controller/method/id

I have defined this route: $route['importador/portes/eliminar/(:num)'] =
'mycontroller/mymethod/$id';
Now, if i enter the URL
http://localhost/mywebsite/importador/portes/eliminar/4 it loads the
correct controller. The content of my controller is echo $id;. And prints
always "$id" instead of 4.
It's my first route so i must be doing something wrong.
Any tips? Thank you!