My daughters 2010 S40 has been giving us breather/vent issues and I finally resolved it. Tried to get help here on this forum but I guess nobody has ever had this issue. If you ever have positive pressure blowing out your oil filler/dipstick and have replaced the pcv breather box, don't forget to check your return at lower intake manifold. I had some vacuum there but not enough to overcome the plastic pcv valve within the oil filter/breather catch can. So the oil was blowing out the filter/breather box at plastic top. I took a can of carb cleaner and sprayed the crap out of the return connection with engine running and that finally gave me more vacuum to suck the fumes through. I now have negative pressure at oil fill cap. Volvo has gone through 3 modifications on this oil trap/filter so if you have the latest one and think it's clogged or blocked don't overlook this return vacuum connector. Hope this helps someone in the future when you're scartching your head going WTF.

 

Thanks for the share - its a good point about cleaning the ports and hoses when doing the PCV kit. Some people recommend doing Seafoam treatment prior to replacing the PCV system, others just suggest to do as you noted - manually clean out the ports when doing the repair.

 

I like how Ford just run a hose from the valve cover to the air filter box. A cheap 1-way valve and a small square of foam to catch the oil residue and she's done. Volvo has been over complicating PCV systems since the 80's.