Oil in Air Intake / Vacuum Leaks - Source???

[hankster66]

The Car: 2000 996 6spd Cabriolet 97k

Prior Work: 2 years, 2k miles ago... Top End refresh, AOS, IMS/RMS, spark tubes, coils, timing, pump, etc.

Recent Issue: After overhauling suspension (probably coincidence) fault codes: P0442 (fuel tank ventilation) and P1130 (Oxygen sensing)

Driving/Engine Experience: Was testing new suspension, driving great on day 1. On day 2, check engine light came on. Was running fine, although I smelled a faint smell of oil.

 

Summary of My Diagnosis...

- Durametric showed two fault codes, nothing else. Cleared codes to see what would happen. Engine immediately idled rough.

- At first everything was leading to fuel/vacuum leak. Gas cap, which is the principal culprit, was fine. Proceeded to smoke test air intake, oil filler, gas filler, etc.

- Air Intake/Throttle:  Disconnected air box and connected smoke to throttle body. There was a bunch of smoke all over the place, It was hard to tell from where, but one place that was obvious was the intake manifold adapter (circled in the pic below). I then sealed the throttle body and pushed smoke through the booster valve. Smoke seem to come from center distributor tube, so decided to remove throttle body and front distributor section. In doing so found oil in throttle (not there before test), and then saw shiny film inside intake manifold (see pic below)... wiped with rag and confirmed (similar to when I tore down the engine for prior work). After removing and sealing openings, identified smoke coming from center of middle distributor tube (pic below).

- Oil Filler:  Sealed the booster valve and smoked filler tube for any leaks there. No leaks from filler tube. But after a while saw smoke come from the previously identified areas, but not as strong. Also now could see smoke coming from the manifold side of the intake manifold adapter where previously could only see from hose side. Again, not as strong as when pushing smoke through valve or intake.

- Gas Filler: So having saved what initially seemed obvious last (as suggested in another thread), smoked gas filler tube to rule out fuel tank bleeder valve. Not sure if bleeder valve failure can be tested with smoke, but no smoke came from bleeder valve or anywhere else, but did come out of opening across from cap (pic below).

 

Questions...

- Oil Sources: I worried when I saw the oil that i have a problem with the new AOS. Could the vacuum leaks noted cause oil to come into the intake? The other item I read that could create issues for AOS and oil in intake is the lower vent pipe connector on bank 2 passenger side. I didn't see any smoke on that side.

- Gas Filler: Not sure what to make here as it relates to the fault codes.

- Is there anything else I need to check or look for to solve for oil in intake or fuel tank fault?

 

[JFP in PA]

We have seen new (aftermarket) AoS units fail right out of the box, which is why we no longer use them.   If the car was in my shop, I would start by hooking up a digital manometer to the oil fill cap and seeing what kind of vacuum you see there; it should be less that 5-6 inches of water, any higher than that and you have found your vacuum leak and the source of the oil in your intake.

[hankster66]

Thanks JFP. You are reminding me that before I did all the engine work, I set up a manometer test. On the old AOS it ran -4.2 inches of water. I nonetheless replaced it with Porsche part as a precaution due to age. I did consider getting an extreme aos, but thought this was sensible along with all the other stuff I was doing. 
 

Would you suggest I put it back together and do the manometer test? Would it make a difference if I did it before/after replacing any of the “leaky parts”?

 

What are your thoughts about the fuel tank vent issue?
 

 

[JFP in PA]

Yes.  I always like to go back to the last thing touched.

At this point, I would not be concerned about the fuel tank as I think you are seeing smoke venting from the EVAP system.

[alex222]

A little oil like on the picture inside the intake and that much on the napkin is normal. It comes from the oil separator. 

[alex222]

P1130 - mixture is too lean so the control is up to the enrichment limit. That's on your passenger side cylinders 4-6. Start with replacing one then the other oxygen sensor on the passenger side. If the error comes back it could be as a leak in the vacuum line but also it can be a leak in the exhaust on the flange where the 3 nuts are. I had on the Boxster the [st*pud] and LAZY mechanics put iron nuts on the exhaust flange after the cat resulting iron nuts corrosion and erosion resulted in sucking in some fresh air to the after the cat so as I noticed the past-cat sensor is super-sensitive sensing more oxygen in exhaust gases more than before the cat = saying 'dude something is wrong w/ your pup' in English. I spent a half-day crawling in the wheel housing removing the remains of the iron nuts from the flange studs on the exaust pipe put the factory nuts by the P/N and that was it and all good since that and that was about 5 years ago.