How to tell if the gas cap is vented. Ordered one for a 66 barracuda. It fits . Car starts easily, idles fine, after driving for 20 minutes or so if you let off the gas or when you’re coming to a stop it wants to cut off . Starts right back up. Drove the same route same speed with the gas cap off , no problem. . Should there be some pin hole on the cap somewhere that vents the cap. Thanks