Jump to content

The RennTech.org community is Member supported!  Please consider an ANNUAL donation to help keep this site operating.
Click here to Donate

Welcome to RennTech.org Community, Guest

There are many great features available to you once you register at RennTech.org
You are free to view posts here, but you must log in to reply to existing posts, or to start your own new topic. Like most online communities, there are costs involved to maintain a site like this - so we encourage our members to donate. All donations go to the costs operating and maintaining this site. We prefer that guests take part in our community and we offer a lot in return to those willing to join our corner of the Porsche world. This site is 99 percent member supported (less than 1 percent comes from advertising) - so please consider an annual donation to keep this site running.

Here are some of the features available - once you register at RennTech.org

  • View Classified Ads
  • DIY Tutorials
  • Porsche TSB Listings (limited)
  • VIN Decoder
  • Special Offers
  • OBD II P-Codes
  • Paint Codes
  • Registry
  • Videos System
  • View Reviews
  • and get rid of this welcome message

It takes just a few minutes to register, and it's FREE

Contributing Members also get these additional benefits:
(you become a Contributing Member by donating money to the operation of this site)

  • No ads - advertisements are removed
  • Access the Contributors Only Forum
  • Contributing Members Only Downloads
  • Send attachments with PMs
  • All image/file storage limits are substantially increased for all Contributing Members
  • Option Codes Lookup
  • VIN Option Lookups (limited)

MkII AOS DIY sanity check

Recommended Posts

Hi guys,

I just removed my AOS ('03 C2 coupe manual transmission) but I fought hard with two of the bolts - the infamous manifold bolt closest to the front of the car and the rear most 5mm allen bolt of the AOS. Any tips on tackling those? My problem is part of the AOS is sitting almost right on top of the intake bolt. Maybe less than an inch above it making sockets impossible. The 5mm allen can only be reached from the top by feel.

I could only put a 10mm box wrench on the intake bolt to back It out blindly (10 degrees at a time all by feel) but when I'm half way, the wrench itself hit the AOS and the bolt can't be unscrewed completely. Using an open wrench may have worked but very difficult doing it by feel. I ended up removing the two 5mm bolts from the AOS so I can lift the AOS and push it out of the way to expose the intake bolt. However, it took me quite some time to find the right extension u-joint combo to remove the rear most AOS bolt. I didn't want to use ball end allen afraid of stripping the 5mm bolt since I don't know how tight it's on.

Any better ways? TIA


EDIT: see photo below. The circled part sits almost right on top an inch above the  front most intake bolt.



Edited by Ahsai
  • Upvote 1
Link to comment
Share on other sites

  • 2 weeks later...

Ok, I just finished this completely and here's my write up. Hopefully it will save the next guy some time. The bottom line is I had to unbolt the AOS first so I could put a socket on the front most intake manifold bolt (not mentioned in other AOS write ups I saw). And you need to get the two AOS bolts from the bottom.

[update 3/14/2015] I did it again today 'cause the AOS failed totally after 1,000 miles (24" H2O crankcase vacuum). I followed the same steps and was able to do it in 4hrs this time including a 15min break. Crankcase vacuum is at a nice 4~5" H2O now.

AOS removal on a ’03 Carrera Coupe manual transmission

1. Disconnect MAF and remove the airbox, serpentine belt, throttle body, and front intake plenum

2. Push the left rubber sleeve all the way to the left, then wiggle the plenum out

3. Remove the alternator (maybe optional but I removed it to get more room)

4. Remove the vacuum line to the intake plenum and the one to the rear reasonator actuator

5. Remove the vacuum elbow and changeover valve on the left intake manifold

6. Disconnect the brake booster vacuum line from the intake manifold

7. Remove the O2 sensor wires from their guiding rails or clips

8. Lower the engine (jack at its strongest point) till it’s resting on the rear subframe cross member and leave the jack there to support it

9. Disconnect the lower AOS vent hose using BOTH HANDS from the bottom

10. Move the vent line out of the way so it’s not blocking the rear AOS 5mm allen head bolt

11. Remove the rear AOS 5mm allen head bolt using a mini-ratchet

12. Remove the front AOS 5mm allen head bolt (a mini-ratchet with a handle that bends downward)

13. Loosen and move the hose clamp on the hose (away from the AOS) that connects to the very bottom of the AOS

14. Unseat the AOS and push it a little toward the front of the car so you can put a socket on the front most intake manifold bolt (otherwise it’s blocking that bolt)

15. Remove the the front most intake runner bolt, then the remaining 5 intake manifold bolts

16. Seperate the rear plenum and remove it

17. Siphon the coolant from coolant reservoir

18. Disconnect the vertical coolant hose between the alternator and the power steering pump (so you can remove the intake manifold from the car)

19. Remove the left intake manifold

20. Disconnect the upper AOS vent hose

21. Remove the 2 coolant lines from the AOS

22. Remove AOS from the engine compartment

AOS reinstall

Reverse of the above.

  • After you connect the coolant lines to the AOS and the vertical coolant hose between the alternator and the power steering pump, you can choose to refill the coolant at this point and do a pressure test (before refilling coolant) to 18 PSIG and see if there’s a any leak at the AOS and the coolant line when things are still apart
  • If you use new o-rings on the AOS vent hoses, apply some o-ring grease on them. That will prevent the dry o-rings from being crushed when inserting into the AOS.
  • Torque the intake manifold bolts to 7.5 ftlb
  • To put the rear AOS allen head bolt in place, you need to manipulate the bolt with BOTH HANDS and be careful not to drop the bolt on the cavities of the engine. It can be very difficult to retrieve the bolt.
Image courtesy of Atlanta Porsche Parts.


Edited by Ahsai
  • Upvote 1
Link to comment
Share on other sites

Thanks! It's a preventive maintenance. The old one had 9yrs/50k miles. Probably can still get some more mileage on it. Crankcase vacuum was fine and the old AOS looks OK but I'd rather replace it now than to deal with smoke, intermix, etc. and scare the sh!t out of myself :)

Link to comment
Share on other sites

  • 2 weeks later...

Thanks for writing this up.

Can you elaborate on point 8 please - lower the engine? Do you mean you undo the engine mounts and drop it down to a cross member? Any other steps involved than undoing the 2 engine mounts?

You don't need to remove the engine mounts. You only need to put a jack under the engine's strongest point and jack it up a little bit until you feel the engine's weight is on the jack, then remove the big bolt from the bottom of each mount that holds the engine brace. Then you can lower the engine slowly and carefully all the way till it touches (barely resting and not putting load on) the cross member. Then you can add jackstands to support the engine.

Link to comment
Share on other sites

  • 3 months later...

Thanks for the write up. 


I stumbled over your write up when I realized that I have a MKII engine and had a write up for a MKI engine. By  then I had the manifold already out. I removed bolt number six with an open wrench and lots of f's.


Suggestion for the write up between step 8 and 9: Remove 10 mm bolt which holds the connector in front of the AOS. Makes it easier to remove the lower AOS vent hose (if you have a weak left hand :blush:)


I got stuck in step 13: The clamp is right against the housing and I can't get anything in there to open the clamp. Do you remember how you did it? It's frustrating as I'm almost done with the disassembly  :cursing: .

Link to comment
Share on other sites

Thanks. That's what I just did. Went to the auto parts store and bought one of those. Wiggled the clamp with a long screwdriver and  attached the clamp pliers from the bottom through the side. Was easy. Now the AOS is (finally) out.


I still have a hard time to understand why I had such a hard time to remove bolt #6. My AOS had the part# 996 107 026 50 which is now replaced with the 996 107 026 51. The 50 part doesn't have the U shaped piece but I still couldn't get the socket on it.


Does anyone has a picture of that area taken from above (from a removed engine) to show how the bolts are placed when everything is in place?

Link to comment
Share on other sites

Oh your AOS is the older version that doesn't have the u-channel as shown in my first post? No wonder you could use an open wrench on bolt #6 on the intake manifold. You should be fine using my steps to reinstall.

Edited by Ahsai
Link to comment
Share on other sites

Done. 5 hours later I had it back together. I'll post later some pictures when I can find them on my GoPro.


Here are my short notes:


- I put the AOS first in and bolted it on (these short ratchet drivers from the link above are very useful) and then the manifold.

- I preassembled the manifold connections to the other bank and slid in the manifold. I wasn't able to put in the two connection pipes in after I had the manifold installed.

- I slid in the manifold with the last screw already in (there is no way to insert the screw after the manifold is in.

- I bought a ratchet ring wrench from Advanced Autoparts (10 mm) and had to cut it to 100 mm (4 inches) length. Additionally I had to grind down the perimeter of the ratchet wrench so that it would fit the screw.

- With the help of the GoPro 4 (and wireless live video streming on my iPad) I was able to put the wrench on the screw head. Was not that bad. Once it's on it was easy to ratch it down.

- Installation of the coolant tank was only possible because the front edge of the black holder was broken. Previous owner or shop broke it. This allowed me to relatively easy slide in the coolant tank,


Special tools needed: cable operated hose clamp plier and the modified ratching ring wrench size 10. GoPro made the installation so much easier.


Now smokeless.


Thanks to all for the helpful tips and how-to's. Especially Ahsai.

  • Upvote 1
Link to comment
Share on other sites

I decided not to lower my engine - I was able to change the AOS on my 2001 996 without doing so. I got to all the AOS bolts and lower connections from below, near the rear drivers wheel, then undid the top clips after I pulled the drivers side manifold out. I guess it was also about 5 hours of work for me too, a fair amount of which was bolting the manifold back on.

Link to comment
Share on other sites

As I said here are some pictures taken with the GoPro. I wish I had them before the project. They show pretty good how it looks like in the back. The wrench shown in the pics only worked for loosen the screw. For tightening I had to modify the ratching wrench.


To unscrew the sixth screw I loosened it with the wrench and then used my left hand but I had to take the fuel pipe between the thumb and first finger. i have short fingers and I barely reached the screw to unscrew it. They turned very easy once lose.


2002 996 MKII engine 3.6 convertible


Admin: Sorry for the many pics. Maybe someone can generate a PDF file out of them. I will try to write something up but next weeks are very busy.






















Edited by Varianti
Link to comment
Share on other sites

I could see exactly what you had to go through for that intake manifold bolt. That's exactly why I chose to not tighten down the AOS first so I could tilt it and put a socket on that intake bolt without any struggle. Once the intake is tightened down, I tightened the AOS bolts from the bottom.

Link to comment
Share on other sites

  • 2 weeks later...

I just replaced the AOS while I had my transmission out on my 2004 4S. Did everything from below, but the top hose clamp was an absolute bear to remove, due to the angle it had been attached (the position of hose clamp ears would not allow access to any tools to open it). I struggled with that one clamp for more than an hour, even with the cable operated hose clamp pliers. In the end, I had to use penetrating fluid and rotate the hose around the AOS connection with pliers so I could get tools to the clamp. Access was very poor.


For the refitting of the new AOS, I used masking tape to stick the rear bolt, socket and extension piece in position on the AOS prior to locating it in the engine as it is tough to get tools and bolts in that hole. I tightened the bolt up then removed the tape and pulled the tools out.

Link to comment
Share on other sites

No, I just removed the transmission as I was going to change the IMS bearing. However, thanks to input from Ahsai and JFP in PA we found that my engine is a later factory re-man unit and it cannot be changed.


If the top hose clamp had been installed 90 degrees around the hose, the whole job (excluding trans removal) would have taken less than 60 mins. All of those hose clamps are tricky, but the worst are those 'squeeze and pull' hose connectors on the end of the rigid plastic pipes. I can never get those things off, I always end up using picks to try and release the locking tabs.

Link to comment
Share on other sites

I have the aos back in and i did have an old version in. There wasn't any oil in the header, but i did have it in the intake tubes.


I have replaced the starter too, that is finally done. Before putting the manifold back on, i have installed the coolant tank. I figured it may be the easiest way to get it back in. It took almost 30 minutes with all of the other crap out.

Link to comment
Share on other sites

HELP!! i can't get the last manifold bolt tightened. It's the one that is right next to the aos. I have the bolt in the hole, but i can't get a socket on it to tighten it. The aos seems to be closer to the manifold than the last one.


Do you think it's possible that the aos is in at an angle or something else?

Link to comment
Share on other sites

Have you tried a short 10mm 12-pt/open wrench? A cheap one from harborfreight is good because it's shorter than the regular ones.

It's unlikely you can use a socket on that bolt with the AOS already installed.

Link to comment
Share on other sites

Btw, you just rediscovered the whole reason I started this thread. I had problem removing that bolt when the AOS was still installed. The u-channel of the AOS is blocking any socket on that intake manifold bolt. You could probably use a wrench but it will be very slow. So I unbolted the AOS and lift it up and that allowed me to put a socket on that intake manifold bolt.

Basically we have two choices, either fight that intake manifold bolt like you are doing now or fight the rear most AOS bolt when bolting down the AOS.

Edited by Ahsai
Link to comment
Share on other sites

I was out there this morning removing the manifold and trying to get access to the aos. The aos bolt closest to the firewall is easiest to remove, but the one closest to the manifold is giving me a ****fit. I am wondering how the f i was able to get it in and out before. 


I don't see how i can get the manifold back on and then tighten the aos bolt. This is really frustrating. i am close to getting it towed to the indy.


The wire harness seems to be providing some access difficulty too.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.