Intermittent engine shutting Off

My car was shutting off often. It will do it randomly and less often than when I first got it. The car had been sitting for a while. Had bad gas but that is no longer an issue. It sometimes sputters and acts like it wants to stall out when I am driving it. I refuse to drive longer distances because of this problem. I really need to know what could be causing this problem. I have used a computer to check codes, the codes it threw were the mass air flow sensor and gas running lean. I fixed that problem. I am just wondering what else can be done to fix this problem without costing me a lot of money? I also replaced the speed shift sensor. Is there more to it?