The 944 Turbo air filter box is seemingly easy to replace. After doing the timing belt and waterpump, removing the previous owner's cone filter and restoring the OEM air filter box was one of the first things I did. Unfortunately, after the procedure, the hood would not close anymore. A long search for the problem began as there were quite a few possible issues that resulted in the hood hitting the filter box. During this search, it was frustrating to see that there are seemingly no complete installation instructions available for the air filter box. Sure, there are many tutorials that show how to replace the air filter itself, or how to remove the box. But none discuss in detail the exact mounting procedure of the box, which is critical in getting the hood to close after reinstallation.
In figuring this procedure out, I had the help of several international forums and its members. Carpokes, however, does require a special mention. The people there, and especially its administrator Tom, helped me crack this with great patience. Thank you for all your efforts! You truly make the Porsche community a better place.

Full procedure

Removal of the air filter box

1. With the hood open, stand in front of the OEM 944 Turbo air filter box.
2. You will notice it has four main elements: the top of the box, the snorkel to the right side that is connected to the top of the box, the air filter itself, and the lower portion of the box.
3. Grab a big flathead screwdriver and remove the two screws that hold the top of the air filter box to the lower portion (number 13 on the PET image below)


The PET shows how the air filter box comes together, yet not in sufficient detail.



This factory Porsche image shows it better. Take note of how the box is mounted.

4. With the same screwdriver, remove the third screw, which sits on the right top side of the air filter box.
5. The fourth screw is partly obstructed by the turbo to intercooler hardpipe. It is easier if you first remove this hardpipe.
6. To do so, first remove the clamp holding the air filter box to the intercooler pipe. Note: many cars are missing this clamp - as is the case with my car.
7. Take a 17 mm wrench and undo the hollow screw that connects the line to the hardpipe. Make sure you don't drop the two washers that sit between the hollow screw and the pipe. If you loosen the hollow screw, you have to replace these washers with new ones. So make sure you have 2 on hand.
8. With the hollow screw removed, undo the two clamps that hold the intercooler pipe to the rubber pieces above the air filter box and on the left side of the lower hood lock.
9. Remove the intercooler pipe and put it aside.
10. With the pipe out of the way, take the flathead screwdriver and remove the final, fourth screw that holds the top of the filter box to the bottom.
11. With the top loose, you can try to grab it and the snorkel, and remove it from the car by pulling up and left. It may be easier to separate the two pieces. To do so, take a crosshead screwdriver and remove the two screws that hold the pieces together. These are located on top of the snorkel.
12. Remove the air filter element.
13. You now have the lower portion of the air filter box in front of you. The AFM is connected to this part, and sits on the right hand side of the box.


The lower portion of the air filter box, with the AFM attached. Take note of how the cable of the AFM runs.

14. Loosen the clamp holding the AFM with a smaller flathead screwdriver.
15. Take a small flathead screwdriver and carefully remove the metal spring clip that holds the AFM connector to the AFM. Remove the connector and put the cable to the side.
16. Take a 10 mm open ended wrench and loosen or remove (depending on how the air filter box is mounted) the two bolts (and their washers) in the front. Note: these two bolts may also be hex-head bolts. Over the years, it seems Porsche updated them to be hexagon head bolts but some cars still have the hex-head bolt version.


Undo the bolts going in the air filter box. Take note of how the L profile is installed.

17. Use the same wrench to remove the bolt (and washer) in the back (there is no L-profile here), on top of the air filter.
18. The air filter box and AFM should now be loose. Take them out of the car and be sure to set the AFM aside in a clean environment.
19. You are now looking at the crossover pipe, see picture below.


The crossover pipe should be straight and not bent.

20. If your mounting hardware is not the same as in the picture above, you will have to remove it.
21. You have succesfully removed the air filter box! To put it back together, refer to the procedure below.

Installation of the air filter box

1. Supposing that your mounting hardware was incorrectly installed, attach it to the crossover pipe as follows: starting from above, put in the 10 mm bolt, a washer, the rubber grommet (which should be pushed through the metal crossover pipe), the L profile, another washer, a 10 mm nut.
2. To do so, I found it best to put in the bolt, and washer first. Apply pressure from the top, and then put in the L bracket, washer, and nut. Use a small ratchet with 10 mm socket from below and a 10 mm ratcheting wrench from above to tighten everything.
3. This is the most important part of the installation as reinstalling the hardware in a different way will probably lead to a hood hitting the air filter box. Make sure to put the L-profiles below the crossover pipe and not on top of the crossover pipe. Also make sure that you point the open end upwards. This will greatly facilitate the future removal of the air filter box.
4. With the mounting hardware installed in the front, put the lower portion of the air filterbox, still connected to the AFM, back in the car. Be sure to slide the AFM correctly into the J-boot so that there are no leaks.
5. Tighten the clamp on the J-pipe to secure the AFM.
6. Re-attach the AFM cable by pressing the connector gently on the connection. Take note of the routing of the cable, shown in the picture above.
7. Put in the two 10mm hexagon head bolts (they are also 10 mm long!) in the front of the air filter so that the bolts sit through the L bracket. Ensure that you place the washers between the L bracket and the bolt, and not the filter and the L bracket.
8. You'll notice that now you don't have to remove these bolts anymore, but merely loosen them in the future to slid out the air filter box.
9. Before you tighten these two bolts, make sure to press down on the air filter box to ensure that the bolts slide all the way down into the L bracket. You want the filter box to be as low as possible. Tighten while maintaining pressure.
10. Take the 16 mm long 10 mm hexagon head bolt, and put it in the third attachment point, on top of the filter box, right side.
11. Your box is now firmly in place.
12. You should clean the air filter box before closing it up. Take a lint-free cloth and wipe it down.
13. Put the air filter back in, be sure to orient it correctly with the higher part (the yellow 'fins') towards the top.
14. Put the air filter lid back on (easier to do without the snorkel attached). As you put it down, attach the breather hose that runs to the timing belt cover if your car still has it. Take the four screws you first removed, and tighten them completely so that the lid is firmly pressing down on the filter, attaching the two parts of the filter box together.
15. Put the intercooler hard pipe back in. Tighten the two clamps that secure the pipe. Re-attach the clamp holding the air filter box to the pipe.
16. Put the hollow screw back in the hard pipe, use two new crush rings.
17. If you separated the snorkel and the top part of the filter box, attach the snorkel by first sliding it in the rubber boot that sits in the fender. Once it's correctly seated, put the snorkel in the top part of the air filter box. Use the two crosshead screws to attach it.
18. You just installed the air filter box in the proper way!


The beautiful sight of a correctly placed OEM air filter box.