Hello !
Probably was loose and with the vibration fall off.
Anyhow replace your PCV VALVE
The Positive Crankcase Ventilation valve is an emissions control device that routes unburned crankcase blowby gases back into the intake manifold where they can be reburned. The PCV system is one of the oldest emission control devices, and also one of the most beneficial. Besides totally eliminating crankcase emissions as a source of air pollution, the constant recirculation of air through the crankcase helps remove moisture which otherwise would cause sludge to form. Thus the PCV valve extends the life of the oil and engine. The PCV valve requires little maintenance. The valve and filter should be replaced somewhere around 30,000 to 50,000 miles
if your pcv its faulty the crankcase pressure could "push out" the oil cap (if it was loose enough.
Good Luck!
SPONSORED LINKS
Wednesday, November 21st, 2007 AT 9:36 AM