new member with a question about mods

Hey there. I have a 1993 audi 90 quattro. I recently put a K&N cone air filter on it and it seems to have lost some power in the upper rpm range. I guess what my question is, would a K&N cone filter cause my car to lean out up top or is it just the fact that it gained more in the mid range that I feel it fall on its face? Would I need a tune after only installing a cone filter?