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Old 08-20-2010, 10:11 AM   #1
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AOS question

So I recently purchased a 2001 Boxster S. Owner recently had a CEL, took it to the dealer who replaced MAF, no CEL anymore. Owner told me about it, and said that the dealer had told him it might be the AOS and to consider replacing. After a couple thousand miles I noticed the CEL had returned. A few days later I noticed a wisp of smoke on startup. The wisp of smoke got progressively worse (bigger). The other day I went out and the wisp of smoke was much more severe. After letting the car warm up for a few minutes I noticed that the smoke had not really dissipated much. I tried driving a couple meters and noticed a flashing CEL, which disappeared (went solid) although the "wisp" turned into a constant stream of smoke.

I'm assuming that the smoke is classic AOS symptom. Problem is that I cannot get an AOS up to Edmonton, Alberta for about a week. My question is whether there is anything I can do to drive the car in the meanwhile (eg, take off AOS and plug the holes).

Thanks for any suggestions.
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Old 08-20-2010, 09:06 PM   #2
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The AOS will not trigger a CEL directly. It is likely that the code is thrown due to unacceptable differences in reading between pre and post cat O2 sensors. It is also possible your O2 sensors have been cooked from all the smoke created by burning oil. Only by plugging it into the computer and reading the codes will you know for sure though.

To answer your question, not much can be done to bypass AOS or plug it up. Driving with the smoke can damage O2 sensors and cats. In saying that, I drove mine in this state for about a week with no ill effects, although I am completely catless and only have one set of O2 sensors. Just remember to check oil daily if you drive it. You may be using as much a 2 quarts per week if it is severe.
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Old 08-22-2010, 04:31 AM   #3
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Blinking CEL is severe. I would recommend taking to a dealer unless you know exactly why it is doing that.
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Old 08-22-2010, 04:26 PM   #4
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A blinking CEL means you correct the problem before driving.

is what I've always read. You need exact codes read without starting the engine again. The standard response has always been "flatbed to a dealers, you have big trouble".

As for "is it the AOS", look at the intake and throttle body to see if the AOS was allowing oil into the intake.

Good luck.
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Old 08-23-2010, 03:04 AM   #5
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Your description of the smoke certainly sounds like the AOS, if not something clearly more ominous. Have you checked to make sure the oil level isn't too high?
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Old 08-23-2010, 04:55 AM   #6
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I would not drive the car in that condition until replacing the AOS.
When an AOS fails completely it can pass enough liquid oil to hydrolock the engine.
Stop the car, order the AOS and install it yourself.
Here's how: http://www.pedrosgarage.com/Site_3/Replace_the_Air_Oil_Separator.html
Happy Boxstering,
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Old 08-25-2010, 08:20 PM   #7
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Ugh

Thanks all for the advice. Especially pedro, your DIY guide was extraordinarily helpful.

So here's the latest. I did not drive the car (though as an academic matter, I still don't understand why one can't bypass.... but now that question is moot).

I did get the new AOS and replaced it today. There was oil everywhere, even in the plenum.

Here's my problem(s). After installation I started the car. There was a TON of smoke initially. I let it run for a minute or two and virtually all of the smoke dissipated. But the engine is now running very rough ... actually it sounds more like a regular miss. I have absolutely no throtle, I cannot rev the engine at all (I did not attempt to drive, just tried to give it some gas to rev the engine ... nada, nothing). Egas IS connected to TB. The CEL is solid, not flashing.



I took a look around for anything obvious and all that I could find was one vacuum line that is not attached to anything ... it is part of a tee that runs to the black and white check valve that attaches to the cross tube (the black and white check valve mentioned in pedro's DIY instructions). I cannot for the life of me figure out where that vacuum line goes (and don't remember disconnecting it?????).

Other than that I haven't yet found anything obviously amiss. Any suggestions, given these symptoms, for what I might have screwed up?

Thanks guys!

Last edited by clueless1; 08-25-2010 at 08:45 PM.
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Old 08-25-2010, 09:01 PM   #8
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The vac line goes to a vacuum reservoir and a switching valve under the intake on the passenger side. Both of these components are part of the secondary air injection system.

This disconnected vac line however is unlikely to be the cause of your rough running problem.

You need to read the codes.
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Old 08-25-2010, 09:16 PM   #9
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the rough running problem is brand new, it only started after I installed the new AOS. And more importantly, ditto the virtually complete lack of throttle (it might have budged 100 rpm with my foot halfway to the floor). I think it has to be something I did not put back together correctly.
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Old 08-26-2010, 11:01 AM   #10
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Quote:
Originally Posted by clueless1
the rough running problem is brand new, it only started after I installed the new AOS. And more importantly, ditto the virtually complete lack of throttle (it might have budged 100 rpm with my foot halfway to the floor). I think it has to be something I did not put back together correctly.
clueless,
could be that the connector for the throttle position sensor is not properly connected..?
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Old 08-27-2010, 12:23 AM   #11
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Well I just took everything off and started from scratch (except the AOS of course). I opened the throttle body itself (4 allen nuts) and saw that one of the very fine wires that made a contact was bent so i straightened it as best i could. I reassembled. As best as I could tell the vacuum line connected to a bigger rubber connector itself connected to a vac line running towards driver side, a bit forward of center. Didn't follow it. Put engine back together. Running fine. Was smoking for quite some time (maybe still is??? not sure how to tell if this is normal after the fact burn off), though not as much as originally still a significant amount. but its driving and all seems well. idle seemed much more steady. for a few minutes at least (or at least so I thought, maybe i wasn't really paying attention / didn't notice???). now she is hunting (1000 rpm to 2000 rpm, perhaps every 5 secs).

Not sure what this could be ... leaky vac line or MAF is what I'm thinking most likely?

Last edited by clueless1; 08-27-2010 at 12:26 AM.
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Old 08-27-2010, 06:55 AM   #12
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You probably have a vacuum leak somewhere still. A big one.
How about the bottom bellows or sleeve on the AOS? The one with the spring clamp.
Also, check that the flex tube that connect to the AOS is "clicked" in. Sometimes they appear to be secure, but are not.
To help you find a leak, with the engine running, you can use a spray can of carb cleaner with the red extension on the nozzle. Spray a squirt around each of the suspect connections.
When you hit the right one the revs will rise because the carb cleaner burns as fuel.
Good lick.
Happy Boxstering,
Pedro

Quote:
Originally Posted by clueless1
Well I just took everything off and started from scratch (except the AOS of course). I opened the throttle body itself (4 allen nuts) and saw that one of the very fine wires that made a contact was bent so i straightened it as best i could. I reassembled. As best as I could tell the vacuum line connected to a bigger rubber connector itself connected to a vac line running towards driver side, a bit forward of center. Didn't follow it. Put engine back together. Running fine. Was smoking for quite some time (maybe still is??? not sure how to tell if this is normal after the fact burn off), though not as much as originally still a significant amount. but its driving and all seems well. idle seemed much more steady. for a few minutes at least (or at least so I thought, maybe i wasn't really paying attention / didn't notice???). now she is hunting (1000 rpm to 2000 rpm, perhaps every 5 secs).

Not sure what this could be ... leaky vac line or MAF is what I'm thinking most likely?
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Old 08-27-2010, 02:26 PM   #13
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I was thinking MAF because this am when I started it up cold the idle seemed pretty stable -- though conversely it did seem like it was quite a bit longer than 15 seconds of stability. By the time I pulled up to the first red light I reached she was hunting again.

Will check the vac lines. Replaced the spring clamp with a screw-clamp on the bellows. Will check that but I was pretty careful putting it on (just because it was a pita to reach and make sure it was secure). Ditto the other vac lines. Will try the carb cleaner idea, i like that idea a lot. (Maybe i'll be able to get my nose able to distinguish between burning fuel / oil?).

Thanks.
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