ORIGINAL: Jeff

Installing a K&N Air Filter -- 2002 A4 1.8t jcraley 2003


1. Remove the entire air intake duct by removing two screws which hold the front end it to the radiator bulkhead and by pulling the rear end out of the Air Box. There is also part of the intake vacuum system attached to the end piece of the air intake duct. This is a small black cylinder about the size of a 35mm film canister which has a rubber sleeve that fits over a tab protruding from the rearward side of the intake duct end piece.
2. You'll need a special three-pronged Host Clamp Pliers (available at any auto parts store which also sells tools) to disconnect a hose that's in the bottom right area of the Air Box (looking at it as you stand at the passenger side of the engine bay). This appears to be the only hose which has a re-useable clamp on it, all the others seems to have non-removable/re-useable clamps. It also appeared to me that this hose must be disconnected in order to get the Air Box open.
3. Audi has made the Air Box on the new A4 much easier to open than on previous models. Instead of four clamps which were somewhat difficult to open and close there is now only two screws easily accessible at the top corners of the Air Box. Just remove these two screws and tilt the Air Box towards the engine in order to access and remove the stock paper filter (you'll be amazed at how much thicker the stock filter is compared to the K&N!).
4. You'll notice the bottom of the Air Box is covered with some interesting looking gray foam rubber sheeting. Leave this in place as it appears to be there to reduce air induction noise, removing it may make the engine induction sound cooler but I'd be afraid of some unforeseen OBD-II problem it might also cause - best not to temp fate. Slip in the K&N filter, making sure not only to put the correct side facing down but that it seats properly in the Air Box, and reverse the process described above to reassemble the air intake.
5. One last note - Audi has added another new wrinkle to the A4 air intake duct. Before re-attaching the end piece of the air intake duct to the air box, take a look inside it. You'll find a specially designed very fine screen pre-filter fitted into the end of the air intake duct for trapping debris which otherwise would make its way into the Air Box and be much harder to remove. An immediately obvious benefit of this new pre-filter, if an air intake obstruction is suspected all you have to do is pull out the end of the air intake duct and check it (those German's think of everything!). Be sure to clean this pre-filter before the final re-assembly and to also check it on a regular basis (I clean my out at least once a month).

I got this from audiworld