My 96 chevy lumina has started sputtering when it first starts. It doesn't do it all the time, but when it does I have to either turn it off and start it again or rev up the engine and let it work itself out. At one point it died and the check engine light came on. It said multiple miss fire. Since then I have replaced the spark plugs with nice plugs, replaced the spark plug wires, changed the fuel filter, changed the air filter, and had the fuel injectors cleaned by big o' tires. After all I did it worked for about a week and it has started doing it again. This car has to last me longer, I cannot afford a car payment and I have a very long commute to work. Please help.