Check Engine Help-System Too Lean

Brief summary of what happened 2002 996 C2. About 2 weeks ago I downshifted hard into a U-Turn and had the famous 996 smoke out the exhaust. I had the oil changed and nothing was seen in the oil to indicate any mixing of metal or water. The oil was completely full and could have spilled over. After the incident I had no check engine lights or codes to report. 2 weeks later I an getting codes: System Too Lean (bank 1 and 2) P0171 & P0174 The MAF sensor was replaced with a Bosch sensor in September of 2019. Most research i have found states O2 Sensors. Could the O2 sensors be dirty from the oil burn off in the exhaust from the previous incident? How do I which ones to replace? The 2 in front of CAT or 2 after? I know this is NEWB question but just trying to get some clarification or any help advice.. Thanks Guys

The first thing I would do is test the AOS. Sounds like you may have just "dodged a bullet".

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what bullet may I have been lucky enough to dodge? Serious question. Checking AOS by way of oil filler cap tomorrow. You don�t think it�s O2 sensors?

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No. Having codes P0171 and P0174 tells me the 02 Sensors are working fine, they both agree with each other, that the engine is running lean. Anytime you have excessive smoking, you have oil going into the cylinders. If about 60cc of oil goes into any one particular cylinder (usually #4) in one cycle, there is a serious danger of hyro-lock that can cause catastrophic failure. We have seen about 6 in this forum this year alone. That's what I mean by "dodging a bullet".. A small tear in the AOS diaphragm causes high vacuum in the crankcase. This high vacuum with high RPM and a u-turn caused the engine to take a big gulp of oil. Continued driving for two weeks with high crankcase vacuum has caused a vacuum leak probably on the AOS bellows if you have a 996.1, possibly on the oil fill tube, or even front or rear main seal. I have had rear main seals on M96's squeal from high vacuum caused by Failed AOS's. The factory AOS has the highest failure rate of any part on the 996, and is pretty high on the list for causing catastrophic failures . ( IMSB is #1).. I know i'll probably get blasted for this, but you should check out my UAOS. It eliminates or improves the deficiency's of the Factory AOS. Good place to start. A Manometer would be a better choice for accuracy, as sometimes the faults can be masked by the rubber diaphragm moving and leaking and not leaking. There are some very frugal solutions in this forum..

And how have you figured that out? I can think of several parts which are prone to breaking. hydro-lock failures or just smoke? Link please.

Definitely dodged a bullet! Let�s hope it�s not any of the main seals and just the AOS. Let me ask you another question. Is the car able to make short drives around town. It�s my only car as I sold my daily driver and I am currently looking for a new daily driver. Would I further damage the car to drive it in current state.

Post Porsche mechanic inspection came up with his normal recommendations. changing of fluid (transmission/power steering etc), car needs rear tires, car needs shocks. Nothing mechanically major like seals or leaked were discovered. hoping just AOS problem

Instead of jumping into any theoretical conclusions. Time to get the engine smoke tested and see if there are any vacuum leaks.

Have you checked vacuum pressure at oil fill cap?

OK well i feel like a complete DUMB A$$. I am obviously no mechanic. So I popped the engine lid to check vacuum on the oil filler cap and it wasn't even on! When the cap was off the car was running and idling rough. When i covered the cap it appeared to balance out. When i put my hand on I felt a slight pull of air and i could hear it as well. I put the cap back on and cleared the codes. Started again it idled rough then balanced out again. I restarted and same result, rough idle then it balanced out. What should i do next? Drive the car and see if CEL comes back on? or just park it and replace the AOS? The main problem is I sold my daily driver and am currently looking for another. is the car ok to drive short distances? Thanks guys

just drive it. I had a large vac leak and got the same codes. As a precaution i would still propery check the the aos. U may have just had too much oil in your car. It should be in the middle of the dip stick. At the top of the dip stick cars have been know to suck oil into the aos on high g turns and smoke the tail pipes. This can hydrolock a motor and kill a it. Sounds like yours is fine but i would double check your level.

I drove the car for 10 miles never getting over 60 and 5k RPMS. It appeared to run fine no loss of power. When i got home i restarted the car and the idle hunted for a second and balanced out fine. When i pull the cap i definetly hear it sucking air and i can make it whistle when i put my hand just right. Could the oil filler cap not being on for a week cause damage?

I can't answer your questions about damage due to the oil cap removed, have to wait on one of the experts there. However, there was mention of AOS testing, and I can add some links for DIY if you are interested in checking whether your AOS is behaving correctly. When you remove the cap, there is vacuum, which is normal, but the question is really whether there is just enough (~5 inches water column) or too much (>6++ inwc) indicating an AOS failure. It sounds like maybe you identified your issue. The following would not address other vacuum leaks or issues, but sudden white smoke is usually an AOS failure (or maybe just oil too full), so if you are interested: These are the first AOS measurement threads I could find, best way is to use an old oil cap, tube/fitting, and a manometer. Especially consider posts from Ashai, who definitely knows what he's talking about. https://rennlist.com/forums/996-foru...-question.html That's a bit of an old thread, and a concise explanation to measure both AOS vacuum, and the Engine crankcase pressure is provided here: https://rennlist.com/forums/996-foru...w-by-test.html It can actually be important to measure both, (pointed out by Flat6Innovations in the Engine-health-blow-by-test thread) since intake vacuum, through the AOS, is pulling vacuum on your crankcase, while Engine blowby (past the rings) is adding pressure to the crankcase. In some cases, they could both be bad (too negative and too positive), but just offsetting each other to make the final number look good! Doing a blow-by test isolates the AOS out of the system, to get the blow-by value; if it's good, then you can probably trust the AOS vacuum number. I'm not implying you have a problem at all, but since AOS failure was brought up, this is a way to measure and check its current operation, if you're interested in a minor DIY measurement. The kit to measure is pretty easy to make, but for the easy way out, TexSquirrel offers a complete kit to measure both in the Marketplace. https://rennlist.com/forums/market/1199553 Good luck!

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Stop taking the oil cap off while the engine is running. Clear the DME adaptations by removing the negative battery cable, wait 15 minutes, re-connect the negative battery cable. That resets all of the engine adaptations (learned engine settings) and returns everything to base values. While you are waiting, best to check the oil filler cap O-ring and make sure it is not cracked. And as said, pull your dipstick and check the oil level. Then go for a gentle 30 minute drive so the DME can re-adapt.

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negative off now and waiting for 15 minutes. will update after drive. Thanks

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I would further suggest that you make contact with the positive cable and the negative cable. I am no expert on this, but presumably this will "drain" any capacitors in the DME that may store energy and allow for a full clean slate.

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ONLY WITH BOTH CABLES DISCONNECTED FROM THE BATTERY!

You guys are all over thinking this. All he needs to do after putting the oil cap back on is to DRIVE it! Nothing else! The DME will re learn the parameters and all will be fine. Just like it learned when the cap was off, it will just as fast re learn when the cap is back on.

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Good call. Should have stated this. Hydrogen is somewhat explosive...

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Technical info :: No, no damage from driving under light load with oil cap off. The engine will run lean and poorly, but no damage if light load -short distances only. IF heavy load or long distance, the lean condition will cause very high cylinder temperatures and damage can/will result. Nick, I know you are looking for a debate/argument, but rather than go on the defense of my statement, I'd rather put you on the defense of your question. Name a part on the M96 that has more failures and can lead to catastrophic engine failure (other than IMSB) than the AOS.,,,.? I'm talking about hydro-lock failures. Search post from DukeTJ8, PDXmotorhead, Theyoung911.In the PDXmotorhead thread you will find reference from Jake and pictures about two more engines with bent rods from hydro-lock, in the Craigslist thread and Roller threads you will find more instances of cars with excessive smoking/AOS symptoms, then catastrophic engine failure. All of them from this year... To the OP;; have the AOS accurately tested for proper function. Don't play around with this symptom. It's like playing Wheel Of Fortune, with one space that says "catastrophic failure"..and the other spaces have less devious outcomes. The accurate test will stop the guess work.

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LOL KaBoom! Once had an instructor show us what we could weld with a car battery. And once, while in the Navy working on my MG, got my wristwatch stuck between a positive terminal under the hood and the body. That fried my wrist and I have the scar to this day.

" working on my MG, got my wristwatch stuck between a positive terminal under the hood and the body. That fried my wrist and I have the scar to this day." ^^^ OUCH !!! Freakish accident ! - you're really lucky you weren't in a combustible situation (like an open gas can or fuel tank nearby...) probably would have been slightly more painful

UPDATE: I obviously reinstalled the oil filler cap properly and disconnected the negative for min of 15 minutes. Drove the car for 60 miles and no CEL!!! I am assuming this fixed the issue. Thanks for all the help and the advise! Nothing like free help and thanks for taking the time to walk a mechanical short bus riding dude! you guys are the best! till the next CEL or issue i appreciate all the help!