New member needs oil leak help

[mtrdrms]

p0172 is almost always a leaky vacuum hose. Is the elbow on the passenger side of the intake manifold, put back in place? That is the most common offender.

Yes. New hose and new clamp fully seated. One of the intake manifold bolts stripped out of the head and it was too cold outside to helicoil. Could it be a gasket leak there?
I thought a vacuum leak would cause a lean condition? It does seem to be a vac leak however as my idle seems high (1000-1100).
Thanks all for the assistance.
Andy

[erikv11]

Yeah the p0172 is a misunderstood code. According to VIDA, it actually indicates a lean condition. From VIDA:

The control module receives information from the HO2S about the fuel/air mixture in the idling and partial load ranges. If the fuel/air mixture deviates from λ=1 the short term fuel trim will compensate this by adjusting the injection timing so that λ=1 is achieved. When the short term fuel trim carries out this adjustment, its mid-point must be adapted by the long term trim. When the long term fuel trim has adapted the short term trim to a maximum value, DTC 2-3-2 (idling range - 0.48 ms to +0.40 ms) or DTC 2-3-1 (partial load range 0.773 to 1.227) and status message Upper Limit (lean fuel/air mixture) or Lower Limit (rich fuel/air mixture) will be set.

So ... P0172 actually indicates a lean condition by advising that the ECU has reached it's upper limit of compensation: It has added as much fuel as it's willing to add to rich up the mixture, but it still seems lean according to O2 sensor feedback.

I took all of this from a very knowledgable poster, it is over at VS in this thread http://volvospeed.com/vs_forum/topic/16 ... fuel-trim/

See also https://www.matthewsvolvosite.com/forums ... 5&start=20 for more speculation. That's why I say "vacuum hose leak" rather than simply "vacuum leak" because the elbow is not always under vacuum. Anyway the p0172 is indeed, almost always a leaky hose.

That's a good call on the IM bolt, that would probably do it. Also, I agree with abscate's opinion on waiting.

[mtrdrms]

Thanks a ton! Seems to run great and holding steady at 20 mpg. Once the warmer weather comes, I'll tackle it.

[mtrdrms]

Ok so I think I fixed the p0172 and wanted follow up with all that helped me. I systematically replaced each vacuum hose and reset the cel. Then I would drive for a while to see if the light would stay off. It finally stayed off with the replacement of the brake booster line. It had a crack near the manifold and the old pinch clamp wasn't strong enough to keep it sealed. New hose and screw clamp and problem solved.
Thanks again.

[erikv11]

Good troubleshooting. Thanks a bunch for following up, really helps out the user base here.