Unscrew the "arrow" bolts from the upper part of the air filter housing and remove it in an upward direction.
Remove vacuum hose "1" from air inlet changeover valve "N335" "2"
Unlock the lower part of the air filter (lightly press the rubber parts on the right and left and remove them in an upward direction). When installing the fastener, do not use lubricants. Disconnect the air duct hose "1" going to the secondary air pump. Item 1: not installed on all vehicles (only with Euro 5). The electrical connector for the air inlet changeover valve "N335" is not installed on all vehicles. Carefully remove the lower part of the air filter housing.
Installation
Use only the original replacement air filter element. Use sealant to install the air intake sleeve (silicone free). Secure all hose connections with clamps that match the standard equipment. If a warm air intake line is installed (only for countries with cold climates), then it is necessary to ensure that the air intake nipple "arrow" is correctly fixed (take into account the markings).
Check the water drain hose "arrow" at the bottom of the air filter for contamination and sticking (clean if necessary). Clean the air filter housing (upper and lower part) from salt residues, dirt or leaves (if necessary, clean with a vacuum cleaner). Check the suction channel up to the replaceable air filter insert for contamination. Reconnect the electrical connector of the air inlet switching valve I335-(if available). Reattach the air duct hose "1" (if available). Install the lower part of the air filter housing. The water drain hose must be laid straight at the bottom and must not be kinked. Reinsert the vacuum hose "1" into the nipple of the air inlet changeover valve "N335". The clip on the air filter insert "1" must be next to the clip of the air filter housing "2".
Carefully place the upper part of the air filter housing without applying excessive force onto the lower part of the air filter housing. Before tightening the bolts, make sure once again that the upper part of the air filter is located in the groove of the lower part of the air filter (air leakage through leaks). Then screw the upper part of the air filter housing to the lower part with bolts. Make sure that the air duct hoses are securely seated. Install in the reverse order.
(This article was previously published on the resource: «AudiManual»)