Just replaced mine but I had no symptoms mainly did it for maintenance and it was cheap. It is fairly easy to do and there are a quite a bit of write ups on it. It took me about 30 minutes for the whole procedure but it was done on my lift. I would imagine that it is much more difficult if you are on jack stands. Except for disconnecting the top hose I did everything from underneath.

Didn't give it a chance :). Was in there doing the IMS so popped a new one in while i was in there. 57k miles.

What is the AOS ??
 

What is the AOS ??

AOS = Air / Oil Separator. emissions device that (obviously) separates oil droplets from the air and recirculates it back to the engine. when it fails the car (usually) smokes like crazy - something from a james bond movie.

http://sites.google.com/site/mikefoc...t/_DSC4817.jpg


airoilseparatorreplacement - mikefocke2
Replace the Air/Oil Separator

It would be interesting if someone put together a spreadsheet of several members' common failures against time and mileage. Maybe driving type too (weekends only, daily driver, track car and so forth)

Just a thought

Juding on anecdotal evidence, it seems like a reason they fail is a combination of age and temperature fluctaions of the AOS.

Hey, my AOS finally failed today! First indication was fluctuating idle and then those BIG clouds of smoke! 1999 with 104,500 miles and 28 track days.

Just replaced mine this weekend. I knew it was going bad. Had all the classic symptoms, smoking, suction on the oil fill cap, rough idle. I had a friend help me and I bought the special hose clamp tool (big help) I replaced the old clamp with a more common 2" water hose clamp.

I have a 2002 Base with 83,500 on the clock. While I was in there I replaced the plugs, changed the air filter, and spray cleaned the MAF. I was a little worried when I first fired it up because it continued to smoke for about 5 minutes. However, it eventually quit smoking. Runs like new now!

I have noticed in reading the above posts that 70,000 - 85,000 seems to be a common denominator for mileage on these.

AOS failure at 42,000 mi
 

My AOS failed at 42,000 mi. 2002S. I blame it on leaving the car jacked up in the rear for several weeks waiting on parts. But it could be coincidence

1999, 50,000 miles on second motor when replaced.

Blue smoke @ start & squeak when hot
 

So my 02 S with 70K has started smoking thick at start up for 60 seconds or so.

I think it's the Air Oil Separator because;

-oil cap is sucked down so hard I can't pull it off with she is idling.

-smoke is gray blue

-when I disconnected hose between AOS and air intake taping both ends she started and idles fine plus oil cap could be easily removed. But I have not tried driving like this.

-hose from AOS to intake was lined in oil

-a week before she suffered misfires for which all coils and plugs were replaced which fixed mis fire. My understanding is bad AOS can fowl up plugs and cause coils to burn up which happened.

-CEL was on with codes for secondary air system as well as mis fire.

-CEL came back after Coil and plugs were replaced I don't know what codes


Strange symptoms(why I think it might not be AOS or might also be additional issues):

-stopped smoking about 60 seconds after start I then try ed driving and she squeaks when giving throttle between 3000 and 4500

-when I pulled over once warmed up she was squeaking loudly at idle (sounds like its from area of watter pump) but after opening hatch behind seats it sounded like squeak could have been internal perhaps not enough oil pressure to lubricate with the vacuum caused by bad AOS

But I still think it may be watter pump because water temp is living a half line above 180deg (I think in past ran just about 180deg) and I need to add 6 cups of watter & anti freeze about every thousand miles.

So I would appreciate some opinions AOS, AOS and watter pump or...

Mine went at about 42,000 (2002S). I have had it about 2 yrs as a daily driver. Just driving normally, I noticed the idle was a bit high and then a huge cloud and a god awful screech. Fortunately I was close to home and drove a about a half mile. After replacing the AOS. cleaning the throttle body (full of oil) and MAF I still get intermittent CEL of 1128 and 1130 which I presume is a vacuum leak somewhere. It occurs every few days (after reset) at the same intersection when at idle waiting for the light.

Mine went at 138500 K's (86,500 miles or thereabouts) Lots of smoke on start up only symptom and not every start up. :mad:

Left it at one of our local STEALERSHIPS for a couple of days so they could induce the smoke. No good, picked it up and they said couldn't find anything wrong and it would cost about $1900.00 to do a proper inspection but then still couldn't guarantee the result. I mentioned the AOS to them and they said they didn't think so.:confused:

Very embarrassing when you start up in a servo after filling up, and it got to the stage I hated taking the car out because I didn't know when it was going to smoke fart on me.
You could rely on it doing it when there were people around to bring you undone.:o

Took to to another specialist Porsche workshop not a STEALERSHIP, mentioned what was happening and he agreed straight away that it is more than likely the AOS. Left it with them overnight, picked it up next day and bingo, problem solved and $400.00 later. Happy with that. :cheers:

That specialist now has all my work and the Stealership has lost it, including services. Couldn't believe they didn't know of the AOS problem which appears to be a common problem.:)

I still very rarely get a small puff of oil smoke on start up, which my specialist said some 986's and some 996 do this, no reason why but nothing to worry about, a little bit of oil in the chambers blowing out on start up, also car would have sat in the garage for a fortnight or so before it sometimes happens. :)