What would cause a car to smoke sometimes but not all the time? Sometimes when I’m driving black smoke (gas?) will just start pouring out like I’m james bond, then it will just seem to go away. It sometimes smokes on start up, and sometimes doesnt. And it sometimes smokes when driving and sometimes doesnt. What do you guys think the problem is? I cant figure out why it would be smoking like crazy one day then the next day absolutely nothing.