S40 (New) Engine 2.4 : P0171 Sys. lean DTC

[organic mechanic]

Oil filler cap was left loose and blew itself off. This set codes P0171 & P0455. The P0455 (MAF) code did not return after cap was replaced and codes were cleared; however the lean code did come up again with active and pending status. I understand that it's a closed vacuum system and a leak can divert the vacuum from the intake manifold into the crankcase if there is a leak or that a faulty oil trap diaphram could be the cause. My question is this: would leaving the oil filler cap off damage the trap diapram? Is there something else I should be checking? Any help would be greatly appreciated. The S40 in question is a 2006 model with 63k miles and a 2.4L engine. Thanks again.

[Mpls Volvo]

Nearly the same scenario has just happened to me and I'm hoping for your guidance to figure it out. My 2006 S40 has has 23,000 miles and runs beautifully. I brought it in for an oil change and after I picked it up and drove three blocks the check engine light came on. I brought it back to the mechanic, they scanned found the code po171. They told me that there was a vapor leak from the oil filler cap that they had left loose. After fixing that free of charge, I left and again the check engine light came on. The code is po171 and they indicate that there may be a "oil trap" problem. Did you find out if leaving the oil filler cap loose/off could damage the oil trap? Any help would be greatly appreciated. I want to make sure I don't end up paying for a problem they created.