hello, new to the site, i love my s4o but i have had a recent problem...so please, if anyone could help me with this problem, that would be great... i noticed a loud howling sound from my engine, then the next day my check engine light came on, it said my oxygen sensor said it was running "lean" the howling sound stops when i remove my oil cap. I was thinking it was the pcv valve, but i honestly don't know... i would just take it to a dealer but first my warrenty has ran out, and secondly... it's wv, not a close dealer within two hours... can somebody please tell me what's wrong, and where i can get the part?

Have the same problem with my 05 S40 with 72,000 miles and regular maintenance. Dealer service advised PCV (firebox). Parts and labor just over $400. They also want to replace the seals that leaked because of the PCV problem and timing belt (oil contamination). I plan to have the PCV replaced only at this time. If the oil leak stops, I will plan on an early timing belt change. I don't see how a PCV problem can permamently damage an oil seal.