Ok so I just bought this car I went out to start it about a week ago and it would start but it would shake and wouldn't go past 2000 rmps when I would rev it. I heard the gas cap makes this problem so I screwed the gas cap in tighter and then it drove fine. The same problem just happened this morning but tightening the gas cap didn't solve the problem....does anyone know what is wrong or has this happened to you?