Download PART NUMBER: 21-681 2005.5-2008 AUDI A4 L4-2.0L C.A.R.B.E.O. # D-670. 1. Preparing Vehicle a. Make sure vehicle is parked on level surface. b. Set parking brake. c. If engine has run in the past two hours, let it cool down. d. Disconnect negative battery terminal. e. Do not discard stock components after removal of the factory system. 2. Removal of stock system Read and understand these instructions BEFORE attempting to install this product. Failure to follow installation instructions and not using the provided hardware may damage the intake tube, throttle body and engine. a. Factory air box system. b. Remove the two screws located on the front of the fresh air duct. c. Carefully lift the back side of the fresh air duct away from the air box. d. Slide the fresh air duct toward the firewall. Remove the fresh air duct from the fresh air scoop. e. Remove the prefilter from the stock air box. This may still be in the fresh air duct. f. Disconnect the mass aiflow (MAF) sensor harness from the MAF sensor. g. Disconnect the metal clips securing the MAF harness to the stock air box. There are 3 clips, 2 are shown in this picture and the third one is in the next step. h. The third clip is located on the firewall side of the air box. i. Pull the MAF wire harness carefully away from the stock air box. j. Remove the plastic rivet securing the air box to the passenger side fender by using a flat screwdriver to pry it off. k. WARNING! (The hose clamp securing the inlet tube to the turbo inlet is under high compression). Carefully use a pair of pliers to decompress the hose clamp securing the rubber inlet tube to the turbo inlet. Move the clamp up toward you and let it compress on a higher location on the rubber inlet tube.