Hey all,

I've been noticing my 2005 C2S would emit a puff of smoke upon startup at times and recently upon poking my head around the engine compartment noticed a lot of sludgy buildup around the outside of the throttle body and plenum area. I also changed my spark plugs yesterday and noticed the threads were all oily when I removed them. The exhaust tips on the car are a bit sooty but not excessively so. This has lead me to believe my AOS is bad, however the research I've done so far says that the unit is bad if either A. the oil cap is difficult to remove, B. when you remove the cap the engine stalls, and/or C. there is strong vacuum coming from the oil filler tube. I just tested this and the cap was not difficult to remove, engine did not stall (idle dropped a little, immediately threw a CEL - clever car!) and there was not particularly strong vacuum coming from the filler tube. As far as I know the unit is original so it certainly wouldn't hurt to replace it as preventative anyhow, but could there be something else causing this? I looked at a parts explosion of the AOS system and it appears there are two smaller secondary separators (Porsche PN 997 107 138 00 or #9 in the diagram) and I've not seen any mention of replacing those in any of my research. Could I possibly test the system for leaks with a nitrogen smoke tester? I just don't want to go on a wild goose chase throwing parts at the car. Any input would be appreciated; track day season is fast approaching and I don't want this to be an issue when that comes!

 

Just replaced mine yesterday. Did it myself and got to say that after experience of battery/started harness replacement AOS wasn't that difficult to replace. From the research I did AOS failure is something not very straight forward to diagnose. I was experiencing smoke starting roughly 20 seconds after cold start which was going away quickly. In my case after removing oil cap idle actually was getting faster. Not sure if that got anything to do with changes I did on my car like softronic tune etc. I'll test it out in a next few days and see if my symptoms went away.

 

Any luck? I just ordered the part; should come in tomorrow. Oddly enough, after pulling the oil cap and thinking the MIL/CEL came on because of it, my MIL/CEL came back after I cleared it a few drive cycles later; P0300 random multiple misfire and misfires in all cylinders but #2. I am now very confused; I changed out the plugs with OEM Bosch FGR5KQE0 and none of the coils appeared damaged; made sure to double-check that everything was tight, and changed my air filter. Rechecked all the hose clamps and connections on the airbox and everything's all there. Car runs great AFAIK but I kind of expect the misfire codes to return. I've only had two drive cycles since clearing it so I'm waiting...

 

I didn't have a chance to drive the car so far. Winter here in NYC decided to show up late and so far we got cold and snowy march. This weekend looks good and I'm planning to do small road trip and will report. Increased suction from crankcase/oil fill is definitely one of the symptoms but in most cases you won't be able to tell without using manometer. Honestly I wasn't sure if my AOS was bad. Since I was able to do it myself cost of it wasn't much to rule it out. My throttle body and hose leading to it from AOS had oil sitting in it which made me think that AOS was defective.

 

I went ahead and replaced my AOS yesterday; not a fun job! I broke both coolant quick disconnects and had to repair them with rubber hose and fuel injector clamps (so far so good; we'll see how this works long-term). The MIL hasn't come back for the misfires all week so that's good. I'm going to monitor my oil level over the next couple months and see how the repair did!