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What year model? How was the MAF tested and proven to be good? Doubtful that both O2 sensors have gone bad at the same time. My bet would be fuel delivery issues or a vacuum leak but that one is also the biggest pain to track down. You can't know the MAF is good without knowing what the parameters are that indicate its proper operation. You can't rule out the O2 sensors without testing them as well. If you are at Autozone for a courtesy scan then I have to assume you aren't equipped for doing a smoke test on it as well. You need a good Indy or your preferred dealership to know more.
If you got a code for one bank running lean then I'd suspect either a bad O2 sensor, fuel delivery problem or perhaps an intake leak on that bank. However since you got it on both banks I would suspect the MAF, fuel pump pressure or vacuum leak. If it is fuel delivery related I would also to expect you to see a code related to fuel pressure as well so that again points me back to MAF or a vaccum leak.
Never had a fouled MAF in nearly 500K miles of Porsche driving, but my Boxster had a number of intake leaks a few due to a failing AOS. So, I'd be remiss if I didn't mention AOS. Not every failing AOS causes a CEL, in my experience just 1 out of 3, but you can't ignore a possible AOS failure.
Another thing to check is the oil filler tube cap. This can leak due to age/miles. With the engine up to temp and idling open the rear trunk and without unscrewing/loosening the cap see if you can just move the cap about or even pull it up a bit. If you can and if the engine reacts that's a bad cap. My 2002 Boxster went through 2 of these in over 300K miles and the cap on my Boxster had a bit of play. Might mention the oil filler tube cap leak was an idle only leak. Above idle the leak became insignificant.
Never had this happen with my Boxster, but the oil tube can crack/split or in some way develop a leak.
The intake o-rings have been known to fail and while I never had any problems with vacuum hoses as Venom51 mentioned there are a number of vacuum hoses which can develop a leak. A smoke test though should alert the tech to any intake o-ring or vacuum hose leaks. Not sure if it can help a tech detect an oil filler tube leak or a failed AOS.
06-27-2019, 06:18 PM
Error Code + Check engine light
