Fuel enrichment both banks are at their limits. Air leak is suspect #1. And given the MY...

Well, the CEL lit up on my way home, the codes seem to relate to a variety of possible faults. The car runs fine at speed, but has a grumpy idle.

Some of the likely candidates are the MAF, or the AOS (air oil separator, which seems to often fail in the 50-80K range), or possibly something to do with the evaporative vapor / vacuum canister.
One source I read mentioned that he couldn't remove his oil cap (sucked down by vacuum), and this indicated an AOS problem. I've never tried that, but yup, it's got a hellacious vacuum.
Anybody got hints on where the MAF and AOS are located? How to get to them? How to test em?
Advice welcomed.

... and the first thing I'd check, if nothing else had been done recently to the car is the OIL CAP.
A bad O-ring or a loose cap can certainly induce an air leak in the system.
Check for the simple issue first.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna




Edited 1 time(s). Last edit at 01/28/2011 09:42AM by Pedro (Weston, FL). (view changes)

miles, phase of moon, etc., AOS has to be considered first as the air leak.

You have to be careful. You may not have much engine run time available to diagnose this if it is the AOS before the thing goes really bad and the engine starts sucking oil and if it does this the engine can suffer from hydraulic lock and this can ruin the engine.

The remove the oil filler tube cap with the engine idling is a good test, but not 100%. But you should be able to unscrew the cap and remove it with the engine running at idle. If you can it may still be the AOS but it might be leaking so bad that the engine crankcase is not under as much negative pressure as it would be otherwise.

If you can't remove the cap, or if it is very hard, AOS has to be either confirmed or cleared, and the sooner the better and teh less (ideally none) engine running the better.

If you suspect the MAF the MAF can be disconnected from the wiring harness the codes cleared (which resets all the learned engine fueling/etc.) and the car driven normally. The CEL may come on due to the MAF disconnect but the P1128/P1130 error codes should not appear. The risk is you might have to drive the car 30+ miles under a variety (but nothing gruesome) ways (stop/go, blvd and highway crusing)) to give the DME adequate time to detect the conditions that warrant P1128/P1130 error codes.

If not AOS, if not MAF, fuel supply (low fuel), fuel pressure then become possible suspects.

But eliminate the AOS first.

My 02's AOS failed around 78K miles and the 2nd one failed maybe at 180K miles. The engine is on its 3rd and this AOS has maybe nearly 60K miles on it.

Sincerely,

MarcW.

Thanx for the quick replys, guys. Uh, sorry i forgot to mention year & mileage (2002, about 70K, non S)

Pedro, Yup, checked the oil cap, but first checked it with engine off when I got 'er home. Seemed secure. Was surprised by the vacuum when running, and I only ran it long enough to recheck the error codes.

Marc, you've been there, done that. (I wonder if anybodys looked into what fails??)

So, today I acquired a new OEM AOS, $186, plus the governors vigorish.
I'll letcha all know of the outcome tomorrow (Sat).
Again, thanx for the advice & knowledge & experience, fellers.
MikeT

fabric/rubber diaphram that developed a small tear/crack. There may be other failure modes.

Sincerely,

MarcW.

Marc now that you have dissected two of the AOS maybe is time to invent the Mark upgrade AOS if that diapharm is weak maybe switch it out its probably worth about 99 cents,.

Well , the AOS was apparently the culprit.
Whattta PITA to change. The worst part was to reinsert the lower tube back into the hole in the engine case. then make sure the bellows was fully seated, the get the dang 10 mm bolts to align and thread in. Arrgh! And damn that Porsche engineer that thought it would be a great idea to put a cable connector and bracket right in the way of getting at the lower bellows clip -that guy oughta be shot.

Anyway, all is back together and the engine idles happily again. No huge suction at the oil filler cap - yes, it inhales air when removed and idle gets crummy, but it's not got a high vacuum like before.

I give great credit to a goood article by MikeFocke2, detailing the replacement. A couple suggestions / tips for improvement:
1. Unplug the cable and connector that blocks access to the lower bellows clip. Remove the bracket (10mm bolt) and tuck the backet/connector out of your way.
2. Cut through the rubber bellows to remove the assembly. Once removed, you can get at the lower clip much better.
3. various hoses and cables get in the way - tie these back with a big tie wrap or something

Thanx again to all for the suggestions and links to helpful sites