On Monday, about halfway through a 900 mile drive, I had my first encounter with limp mode. On I-90 in northwest Ohio, I stopped at a rest stop. When merging onto the highway, a truck in the right lane didn't move over so I had to really get on the accelerator (it wasn't all that close). At about 5000 rpm, I heard what I thought was a backfire and a few seconds later the car went into limp mode. No other lights came on. Since I was able to maintain a reasonable speed, I kept going until the next exit. Turned the car off, let it sit a little while and then restarted. Check engine light.

I was in a very small town but found a mechanic. They scanned the codes which led them to the culprit: the air pipe going into the throttle housing (the one after the pressure sensor) had been blown off at the throttle housing. What I'd heard was a "pop" caused by that rather than a backfire. Nothing was damaged so they reconnected, cleared codes and I was on my way.

I returned home yesterday. Today I scanned for codes and found none. Then I looked under the hood. Under the pipe that had come loose, there was some oil that wasn't there before the trip. Not a large amount but enough that there was some puddling in a recess for a bolt on a mount below and some general oiliness on some surfaces. The underside of the pipe was oily at the upstream end. My first thought was that the valve cover was leaking but there is no evidence of that. Then I checked the PCV diaphragm and it is in good shape -- no tears or cracking.

I removed the offending pipe, cleaned everything up and reinstalled. The car runs great but I don't know where the oil came from. Could it be a bad PCV valve? Any other ideas? Thanks.

Photo with the pipe removed.

 

Since returning home last Friday, I've driven maybe 50 miles (still working from home due to the pandemic). Today I checked the pipes from the airbox to the turbo and from the intercooler to the intake. Both are clean -- no oil to speak of -- so I'm still confused by the oil I saw in the photo above.

Has anyone here seen this before? I would really appreciate any information. Thanks.