My Nissan altima has trouble starting when its cold it shakes a little and turns off once its on it runs good, what's wrong with it?

Try this little trick to see if its pump or injectors. When you get in the car just turn the key to the on position, do not start the car. Do this a few times this will allow the fuel system to pressurized then start it, if the starts right away then its the fuel pump or maybe the injectors are bad...