1.Put the car on flat ground, in park, or first gear with the ebrake engaged. Jack up the rear of the car with a floor jack or bottle jack using the rear jack points. Place jack stands or cribbing under the control arm. Remove the rear tires. It is good practice to place the tires under the pinch seam of the car as a safety measure if a jack stand moves or fails. 

2. Place a piece of tape on the OEM valence, roughly in the center. Then measure from each side to find center and mark with a pen on the tape. 

Your center mark should be at the tip of one of the diamond ribs in the valence. 

3. Open the diffuser box. Remove the packaging. With the machined pockets of the baseplate facing up, slide the fins onto the baseplate until they lock into place. The fin hole should be on the top.  Install the black m4 bolt with a phillips head screwdriver. 

4. Use the notch in the baseplate to center the diffuser at your center mark on the tape. 

The baseplate should be tight to the rib on the OEM valence. 

5. Clamp the diffuser into place on each end, or have someone hold the diffuser in position for you. 

Press the diffuser forward as much as possible to keep it tight to the OEM valence. 

6. Check the left/right position of the diffuser one more time after clamping. Adjust if needed to center it. The inner edge of the diffuser should be almost touching the rib on the OEM valence across the whole width of the diffuser. 

Then drill the center hole, and install a countersunk m6 bolt and nut. 

7. Next, check that the top side of the diffuser baseplate is tight to the OEM valence. 

Drill the outer bolt holes and install the m6 bolt and nut. Once both edges are bolted on, the clamps can be remover. 

8. Drill and install the last four bolts. 

1. The spats are left / right side specific. The countersunk holes will be on the bottom (bottom shown in picture above). 

The narrow end of the spat should be closest to the wheel well. 

2. Depending on the trim package of your Jetta, it may or may not have a tray covering the cavity between the rear control arm and bumper on the passenger side (blue line). 

3.  Remove the 2 OEM screws that retain the tray, if your car has them (white arrows). 

The furthest forward screw can be left in place (red arrow). 

4.  On the passenger side:

Insert the silver torx screw through a washer, then through the spat, and place a spacer on the inside. (countersunk holes in the spat should be on the side with the washer)

5. This will be the same for the 4th hole back, from the narrow end of the spat. 

6. Hold the spat in place. The front edge should be flush to the wheel well. 

Begin to tighten the two torx screws. Move the spat inward or out to ensure that the screw is going through the bumper hole, and into the sheet metal tabs that are clipped around the OEM tray.

7.  On the driver side:

Line up the spat on the car, the front edge should be flush to the wheel well. Move the spat inward or outward to line up the countersunk holes in the spat with the holes in the bumper. 

8. Slide a bolt into the front countersunk hole of the spat (second hole back on the narrow end that goes closer to the tire). 

Place a spacer on the bolt, then slide the bolt into the bumper hole. If the bolt does not fit into the bumper hole, use a 5mm or 3/16" drill bit to enlarge it. Loosely thread on a nut from inside the bumper. 

10.  Drill out the rearmost hole in the spat with a 5mm or 3/16" drill bit. Insert a countersunk bolt, black spacer between the spat and bumper, then thread on a nut from inside the bumper. Repeat on the opposite side. Now tighten all 3 spat bolts.