aaks38

Just replaced the AOS in my 07 4S with about 75k on it. I really had no bad symptoms other than noticing some oil puddling on the intake sleeves which made me think its on its way out. What i came to realize is that the oil mist that does make its way into the intake tends to collect at the upper couplers as there is a disjoint where coupler meets the intake and the oil tends to puddle there.

I followed the pelican parts steps in that:

1. Remove airbox.
2. Undo serpentine belt.
3. Undo 4 screws on throttle body.
4. Undo 4 clamps on intake sleeve coupler and remove coupler.
5. Repeat for the second coupler directly behind the first one. (optional)
6. Remove AC compressor by removing 3 bolts (the one behind is hidden and was difficult to find they are E12 bolts).
7. Remove intake sensor on passenger side manifold by pulling straight out.
8. Remove power steering reservoir by undoing 1/4 turn lock.
9. Remove 2 coolants lines and 3 plastic lines leading into AOS. Coolant lines have a detent that needs to be pressed in, the three air lines have squeeze tabs which need to be pressed and carefully pulled off.
10. Remove 2 screws holding AOS to bracket.
11. Remove 2 screws (T30) holding AOS bracket to block.
12. Once bracket is removed, the AOS will slide right out.

Took me about 5.5 hours although i struggled to find the 3rd ac compressor bolt and had a hard time getting one of the AOS fittings off. You do not need to remove the intake manifolds at all as noted in the AOS DIY of this forum. If i had to do it again, could easily do it in 2.5 hours or less. The part number for the 06-08 S versions is 99710703800 and i got mine from parts container for about 185 bucks. After removing mine, i cut the diaphragm cover off and couldn't see any wear or cuts in the diaphragm as some have observed. However after putting the new one, my engine idle is super smooth and I'm noticed a more deeper sound from my engine/exhaust system.


Thought id pass along in case anyone decides to do it. I believe RND engines recommends replacing this part every 40k or so.

Hella-Buggin'

NIce. My failed on the track and I had to get towed home from five hours away.

Ben Z

Did you replace the tubing also? My RND came with a new AOS but the local shop who installed the engine didn't bother to change the original tubing to it...plastic was brittle from age and heat and developed an unseen crack when reinstalled...vacuum leak, had to be redone after.

linderpat

Nice work. I'd love to do mine, but as a non-S, the process is a lot more involved apparently. I think the engine needs to be dropped.

geeky

Wanted to bump this. About to do my AOS, which tubes are you specifically talking about?

Uwon

aaks38

Tubes 5,7,8 are the ones that can become brittle with age. Mine were fine even after 11 years, however you have to be careful when removing them and ensure to pull by the connector squeeze tabs and not so much the tube...13,14 are the coolant lines and come out pretty easy as they have push in detents, just push in and pull straight out..

user 72902

I replace my AOS ever 4 years along with the water pump. When I add oil I normally do not go to the top bar to prevent the chance that excess oil might end up in the AOS.

Uwon

rtl5009

geeky

yes it can and is one of the primary symptoms of a failing aos

TV911

I have some symptoms of a failed AOS, so I'm wondering if I should replace it. If I start the car and only move it a short distance (not letting it come up to temperature), the next time I start it I might see a big cloud of white smoke. This has happened a couple of times, so now I am careful to let it run for a while whenever I start it. Kind of a P. I. A. I'm also experiencing the dreaded hesitation occasionally when I start to accelerate in 1st or 2nd gear (pretty much full power loss until I get off the gas and go again... then it runs normally). This might be a dirty Mass Airflow Sensor, which could have been contaminated by a failing AOS (I will check that next, and clean it or replace it). I've read that if your AOS has failed, you'll get something like 9-12 inches of crankcase vacuum. I just set up a slack tube manometer, connected to a hose barb mounted in a new oil filler cap (sealed with epoxy). I measured about 5.5 to 5.75 inches of water (after letting the engine come up to normal temperature)... which is normal. So I'm scratching my head a bit.

A couple of you feel that the AOS should be changed regularly as preventive maintenance. I've got about 88,000 miles on my 2006 C2 Cabriolet (non-S), and as far as I can tell from the maintenance records, the AOS has never been replaced. Is it worth going through all the effort if the crankcase vacuum is in the normal range?

jhbrennan

This is not unusual behavior for the flat 6 - search and you'll find lots of discussions about this. It may or may not be related to a failing AOS. Your vacuum test seems to indicate AOS is OK.

aaks38

I would say go ahead and do it given your mileage. Mine seemed ok upon removal but I noticed a difference after putting a new one as the car seemed to idle fine, seemed zipper and the engine note slightly changed as well. Best of all, I have had zero oil consumption after 1k of driving.

I know with many regular cars, back in the day you would change out the pcv valve as preventative maintenance, and the AOS is essentially the same. It is pricey but if you can DIY, go ahead and do it as I think its worth it given that it seems to eventually fail.

White smoke can be caused by the AOS, 0w-40 oils and just the nature of the boxer engine...hard to pinpoint. I don't have white smoke after the new AOS but also run 5w-40, which seemed to also have helped..

TV911

OK.. thanks. To get rid of the hesitation my next step will be to remove, inspect and clean (or replace) the Mass Airflow Sensor. If it's still hesitating after a clean MAF, I'll change the plugs and coil packs. I can't see how the AOS would cause the hesitation issue, other than by allowing oil vapor into the intake, contaminating the Mass Airflow Sensor. But I'll do whatever it takes to get rid of this problem.

I use Motul 8100 X-cess 5W-40.