Collapsed Oil Fill Hose

My AOS seemingly failed on my 60k mile base 987.2 Boxster (rough idle, smoke on startup, wet spark plug threads), so I replace it tonight with a new one. To check my work, I ran the car with the engine cover off and noticed the oil fill tube collapses when the car is running. I'd also say my idle seems greatly improved, but not perfectly smooth. Any suggestions for what to check next or any troubleshooting I can do? I assume this isn't normal. In an effort to clean out the oil from my intake, I took a bunch of things apart from the top of the engine, but it was mostly intake-related. So, not sure why I'd still have so much vacuum in my crank case. Thanks!

What happens if you take off the oil fill cap while the engine is running? Who made the replacement AOS ? I seem to recall having this conversation before with you, perhaps you posted in another thread? The aftermarket AOS units don't have a great reputation. It is not unknown to have a bad one out of the box, but - if your symptoms were identical before and after replacement it's likely not the AOS causing the issue. The .2 engines aren't known for having the AOS fail. It seems much more robust than the 1. engine's version. Wet sparkplug threads are not an indication of a bad AOS. If anything, the additonal engine vacuum would tend to keep oil from leaking around the spark-plug-well seals, which is the only way theads on the plugs would get wet. If the iginition area of the plug was crusty and/or oily - that could be a sign of a bad AOS.

Thanks for this! I posted on Facebook, but the replies weren’t great - mostly people suggesting I screwed up the install or used some knockoff part. I just replaced it three days ago, so I don’t know that we’ve spoken about it. I did follow up on someone else’s post here about increased crankcase vacuum. Anyway, I do really appreciate the help. - If I take the oil cap off when it’s running, it starts to run horribly. Stumbling as if it’s going to die. This is after the AOS replacement. I didn’t try this before replacement. - It’s a genuine Porsche unit from Pelican Parts . - As part of going through this new to me car, I pulled the plugs and borescoped the cylinders. The plugs were replaced 2k miles ago (according to service records). All had their threads completely coated in oil (and/or potentially anti-sieze; it was a little sparkly). The plug wells themselves were dry and the body of the plugs were dry. The pistons had some carbon buildup, including wet spots below the intake valves. The symptoms that led me to replace the AOS were that on cold start, the car would smell like burning oil and gas (as if running rich), would smoke a bit but not a ton, and had a rough idle which would cause the whole car to shimmy until it warmed up, and even warm it shook a bit. Otherwise it seemed to run well and the oil level stayed consistent. When I did the AOS there was oil residue in the tube to the intake. I ended up removing the intake system from the MAF to the plenum to clean it out. There was pooled oil in the plenum and a good bit of oil residue throughout the intake. But, maybe some of that is normal? The car has 60k miles on it. After replacing the AOS , the idle does seem better. It’s still smoking a bit and smelling like burnt oil, but maybe it needs to burn everything off. It’s really that collapsed hose that’s got me wondering. Thanks again for your help!

The oil/anti-seize was likely on the plug threads when they were installed. That's not a good thing, the plugs rely on a metal-to-metal interface to transfer heat from the plug . With an insulating layer like anti-seize (or oil) they are going to run hot (and the white insulator in your photo indicates that's probably been happening.) If it was me, I'd clean all the liquid off the plug threads and then use a rag around a stick and some brake-cleaner to clean out the plug bores in the heads. You want dry metal to metal. The plugs have a plated coating on them (I believe tin) to help avoid seizing in the heads. I admit to being puzzled by the collapsed hose. It is vaguely possible it was damaged/weakened by the failure of the old AOS (if it failed) and normal crankcase vacuum is enough to now collapse it. The fact that the symptoms improved after replacing the AOS indicate there was very likely some issue with the old one. I'm not familair enough with the flat-6 emissions control circuits to say if there is possibly another spot where a component failure would cause high engine vacuum.. but as a suggestion - actually measuring the engine vacuum might give you a quick answer if there is an actual issue. This is done by replacing the oil fill cap with a cap fitted with a vacuum gauge .. the designed vacuum number is floating around on the web, an AI engine would likely turn it up.

I really appreciate all the info. So, it would be ok to gently clean the plug bore threads in the head? I thought about that, but was a little worried about potentially knocking some dirt, carbon or something else into the cylinder. I guess I could be super careful about it. That was my thinking on the hose as well - it being weakened from the high vacuum introduced by a failing AOS . I may replace it and see if the new one collapses as well. And/or I’ll take your advice and build a testing tool with a manometer and spare oil cap to check crankcase vacuum. To your earlier question, what should happen when you remove the oil cap from a healthy MA1/9A1? Would you expect it to start stumbling and almost stall? It sounded so bad I sprinted to shut it down ASAP, as I didn’t want to let it run that lean. That said, maybe it would haven seen the 02 values change and/or dropping RPMs and corrected itself.

I'd expect momentary stumbling, but I am not sure if the ECU can control mixture enough to compensate for a massive crankcase vacuum leak. So - unknown, dunno if I want to try it..

@NateS1 - anything to update here?

I need to get back on this. The car has been driving fine since the AOS replacement so I haven’t been to bothered to pursue it. I am planning to build a manometer to check crankcase vacuum. That should help figure out if it’s a weak hose or if there’s something else going on.