What causes a car not to stay running/
It turns on and then quits after 20 seconds.
Air filter, fuel filter any number of things.
perhaps its cold, or the mixture is too rich...
its getting to be colder out, pump the gas a few times get it revved up. if it still powers down, your car might not be getting enough full intake, problem with lines
Lack of fuel. Could be the fuel pump, clogged injectors, leaking fuel lines, fuel pump relay switch, or something along those lines... :)
alternator bad? is battery dead? Is battery voltage staying above 12 volts when running?
it could be carbonated spark plugs or a dirty throtel body or carburator depending on what you have how old are your spark plugs and wires