Air oil separator question

I know I know, already did a search and now I am more confused. I don't work on my 996 much, so don't know as much about them as the 993s. I just get in and drive it everyday, rarely ever opens the engine lid. Please help me verify if I am on the right track Is it correct if I have an air oil separator issue I will probably see a lot of white smoke etc - In my case with my 100,000 miles 99 C4 I am not seeing that, so that means my AOS is ok? I also read that there is a possibility the bellow that connects to the AOS could be cracked which would set off a check engine light - In my case I regularly get a 1128 1130 code, which I believe could be MAF or other issues. Could this code be caused by a cracked bellow? My idle is fine, fairly smooth. The AOS is located on the driver's side rear engine compartment which requires intake removal to get to? Same with the bellow? Why would someone recommend me to replace the AOS while I am dropping the transmission? Looks like it is two unrelated jobs. TIA

the AOS is in plain sight when the transmission is out... I wont say its "easy" to replace while you are in there... but much much easier than other times. They run about $100-150 for the parts and since the car is older, if it has not been replaced.... it WILL FAIL sooner or later. They have internals that just degrade over time... its good insurance. not ALL AOS symptoms are the white smoke. Sometimes they cause crankcase pressure to be high or low, and a vaccumm leak, oil seapage, water drips... there are several cases... The bellows comes with the new AOS, use the stock clamp (BIATCH to install!!) but it wont cut the bellows like a worm clamp will....

they also made improvements.... new is on the right. IMG_0011.jpg

Those were the same codes i got on my boxster when the aos went out but i was also told those would go on if there was an air leak in the system such as a cracked bellow or oil filler tube.. I heard changing the aos on the 996 was a pain in the butt... on the boxster on the other hand was about a 1 1/2 hour job..

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My experience with AOSs is with my Boxster and the several AOSs it has gone through over the miles and years, but I think my experience of some value here. An engine emitting billowing clouds of oil smoke with or without other symptoms or even a check engine light is almost certainly an AOS. At least I'd eliminate the AOS before continuing to diagnose further and this includes starting and running the engine. P1128/P1130 can be preliminary signs of a failing AOS. I drove almost 1200 miles after getting these errors once a day (over the span of nearly 2 days) before the AOS advanced to the smoking stage on the first start of the 3rd day in a motel parking lot. These error codes can also arise from a leaking oil filler tube cap, a MAF problem, a cracked oil filler tube, and a leaking AOS rubber bellows hose, to name just a few of the more common possible causes. Absent any consistent/constant smoking up startup or any other engine symptoms your car's AOS probably ok. At 100K miles if it is original I'd consider replacing it though the cost for a 996 AOS R&R is higher than that of a Boxster AOS R&R. The 1st AOS lasted around 80K miles. The 2nd around 100K miles. The 3rd has 54K miles on it and no apparent symptoms. If you are having the transmission removed unless you are on a very tight budget I'd seriously consider having the 100K mile AOS replaced "while you are there". When I was getting P1128/P1130 from my car from what proved to be an AOS at about the same time the CEL appeared the engine gave a bit of a stumble. Not much but noticable cause the engine otherwise runs very smooth. Both times this occurred as I had exited a freeway and was sitting at a stop light. When these error codes were coming from what proved to be a leaking oil filler tube cap there was no engine reaction at the time the CEL appeared nor at any other time. If you believe the MAF is involved clear the error codes, disconnect the MAF from the wiring harness and drive the car as you do when the error codes appear. Allow around at least 30 miles of driving. If CEL comes on read the error code(s) to verify they are the P1128/P1130 codes and not one possibly triggered by the disconnected MAF. Do not clear this MAF related error code. Give the P1128/P1130 codes time to appear if they are going to appear. Sincerely, Macster.

Ed, Thank you for the picture and reply, it is much clear to me now. PET shows it requires two AOS? Where is the other at in the motor? Macster, my CEL 1128 and 1130 issue has been around for 50k miles, it comes and goes. I do notice an improvement if I clean the MAF, typically it will come on once for every tank of gas, usually immediately after very rough road driving. My 996 uses very little oil, and never smoked on start up nor hesitation. The only issue I can not resolve is a hard starting problem when it is heat soaked. Meaning the engine will require much longer cranking before it will catch, only happens when it is heat soaked for couple hours.

Ed, did you clean you motor with a tooth brush? That's the cleanest motor I have ever seen.

shhhh, thats a Cayman motor all I could think of was this scene.. http://www.metacafe.com/watch/yt-SXn...your_dog_bite/ tell me, does your dog bite.... NO dog attacks i thought you said your dog did not bite That is not my dog

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Now that explained why the shifter cable is from the wrong direction, I was wondering about that.

edit ^^^^^ added a crack up vid link

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Did you see my question regarding the PET showing qty 2 of the AOS? Nevermind. I had the wrong part number, I was looking at 996-107-023-55, the correct part number is 996-107-080-54 which only calls for qty of 1

I replaced my AOS when I replaced the clutch, RMS, IMS bearing and other items at 105K. I suspected it was bad, but had none of the usual symptoms. I opened it up later on and it did have a 1/2 inch crack in the internal diaphragm. The AOS is a very good thing to replace while you are there items. Rick 99 996C4 87 944S

Rick, thanks. So any other while I am at it crap?

The AOS is part of the emissions system, and similar to a PCV valve. It recovers blow-by gasses from the crankcase, and vents then back into the intake for recombustion, while keeping the oil in the crankcase. Usually. It's also very fragile- a super-thin rubber diaphragm pressing on a couple bits of plastic and coil springs. When my AOS failed, I had no white smoke, just a horrible noise that sounded like a failed bearing or the belt slipping, but was actually the failed AOS putting the crankcase under vacuum, and forcing air past the crankcase seals. A good indication of this is that the oil filler cap will be very hard to remove while the engine is running. A did end up with a bunch of white smoke/oil in the intake when I pulled the cap to see if the sound had stopped. Got oil everywhere when it happened. Ran rough on startup with a cloud of smoke for a few days as the oil from the intake burned out, and also the secondary air injection pump (another mostly pointless emissions thing) which is still throwing a CEL 3 weeks later from the residual oil.

Robin, I also replaced the water pump, vario-cam pads, 1-3 and 4-6 chain guides and all three chain tensioners. The engines now start up much quieter then before as both IMS and 1-3 tensioners were badly scored. Rick 99 996C4 87 944S

Rick, Did you change the chain guide with the engine in or out?

I dropped the engine, as I knew it would make it much easier to pull the cam covers. Here is the link to the post. https://rennlist.com/forums/996-foru...ance-105k.html Not sure what happened to the pictures. Rick 99 996C4 87 944S

Robin, Now I am confused. I need to replace the AOS on my 2002 C4S. Pelican tells me I need two 996-107-080-54. On the other hand, my mechanic, the diagram I have in hand and Stuttgart Classic parts say I need one 996.107.023.55 or 996.107.026.51. Please help figure this out (?)