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johnsonj
 
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Join Date: Sep 2014
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My AOS Failure Symptoms

I know this is a common failure, wanted to post my experience hoping any insight might be beneficial to others.

Two days ago my 07 Cayman S started having a fluctuating idle after a long day of driving.

At home, I checked through Durametric, a lean condition was noted on one of the cylinder banks.

The next morning I took the car for a quick drive, everything fine at first, then fluctuating idle started again when everything was up to temperature.

When I pulled into the driveway the car started running roughly. Real time in Durametric showed multiple misfires on cylinders 4, 5, & 6.

After pulling the engine cover and starting the car it was easy to hear a vacuum leak (by now the check engine light was on due to the misfires).

I found the oil filler tube (the tube circled in red) was completely collapsed when running from the vacuum.

Pulled the piping for the AOS and found a lot of oil inside.

A new AOS will be delivered tomorrow - I'm fairly confident this is my problem. If not, I'll continue investigating.

A plug change and other cleaning is in order also since I believe enough oil was sucked into the cylinders to foul the plugs, strangely, it was only cylinders 4, 5, 6.

I did not have any puffs of smoke from the exhaust during the failure.



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Old 06-17-2018, 07:11 PM
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johnsonj
 
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As a follow up, a new AOS resolved my issues. Although I haven't taken the car on an extended drive yet, I have no more misfires or collapsed oil filler hose.

To confirm I cracked the old AOS open and found the tear.
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Old 06-21-2018, 03:56 AM
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glad you figured that out easily.
Old 06-21-2018, 05:28 PM
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Thanks for posting this version of AOS failure. I experienced the far less subtle plums of smoke version on my '03 Boster S @ about 65k miles.
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Old 06-27-2018, 05:41 AM
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johnsonj
 
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Tonny911Z - no problem - mine failed rapidly, at around 72K.
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Old 06-28-2018, 04:49 AM
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My car has a sort of lumpy idle, and very occasionally has smoked on startup, usually after not having been driven for a while. It also has a bit of a smell of burnt oil after a hard run. Are these possibly symptoms of an AOS on the way out?
Old 06-29-2018, 07:02 AM
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Quote:
Originally Posted by feeshta View Post
My car has a sort of lumpy idle, and very occasionally has smoked on startup, usually after not having been driven for a while. It also has a bit of a smell of burnt oil after a hard run. Are these possibly symptoms of an AOS on the way out?
Test the engine case vacuum level at the oil fill cap, if it is over 5 inches or water (fully warmed up), you will be the first to know.....
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Old 06-29-2018, 07:06 AM
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Originally Posted by JFP in PA View Post
Test the engine case vacuum level at the oil fill cap, if it is over 5 inches or water (fully warmed up), you will be the first to know.....
How does one go about doing this? A quick search didn't turn anything up, but I may not be using the correct term.
Old 06-29-2018, 07:11 AM
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Originally Posted by feeshta View Post
How does one go about doing this? A quick search didn't turn anything up, but I may not be using the correct term.
You need a digital manometer (about $40) and a modified oil fill cap. Search other Porsche related websites, been covered many times.
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Old 06-29-2018, 07:54 AM
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Quote:
Originally Posted by feeshta View Post
How does one go about doing this? A quick search didn't turn anything up, but I may not be using the correct term.
You need a digital manometer (about $40) and a modified oil fill cap. Search other Porsche related websites, been covered many times.

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Old 06-29-2018, 07:56 AM
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johnsonj
 
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Quote:
Originally Posted by feeshta View Post
My car has a sort of lumpy idle, and very occasionally has smoked on startup, usually after not having been driven for a while. It also has a bit of a smell of burnt oil after a hard run. Are these possibly symptoms of an AOS on the way out?
On my car, for testing, I plugged the hose from the AOS to the intake manifold - in the first pic, it has a yellow "dot" on it. After plugging it, my symptoms disappeared.

This was only for testing, to bypass the AOS, and and determine if it was the culprit - I only started the car (no driving).

*If you plug the hose, be sure to use an adequate plug, something which won't get sucked into the intake when you start the car.

If I would have had a manometer I would have used it instead.

Hope you find the cause~!
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Last edited by johnsonj; 06-30-2018 at 06:46 AM..
Old 06-30-2018, 06:36 AM
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