98 S70, 125K. It just started emitting exhaust odors through the HVAC vents, when idling at a traffic light. It doesn't do it on "Recirculation" mode, only when fresh air is selected. I have changed the cabin air filter and the "flap" under it works fine. I can't figure this out, as it seems that the only place the air enters the HVAC system is on top of the cowl, where the cabin air filter is. The cowl is sealed to the hood, so it seems unlikely that underhood odors could be getting in. I don't see or smell any fumes with the hood open & idleing. I have checked the intercooler, piping, turbo, exhaust manifold, etc and do see, smell or feel any leakage. I do not see or hear any exhaust leaks anywhere along the length of the exhaust system. I am stumped.......