My daughter and I had a close call in a P92 with CO. In that case it was due to the removal of the rubber bung in the underside of the fuselage that allowed access to the MLG bolts. A bit of duct tape provided a temporary fix.
With window vents closed it appears the P92 has a negative pressure differential that sucks stuff into the cabin. Open the vents the situation changes.
This may not be relevant to the P2002 but do look at the exhaust/oil staining on the underside of the fuselage and check for any small holes where exhaust could enter in those areas.