Rough Start

[Jeanius]

Recently my car began starting rough after one day of sitting. If i am running the car everyday it starts up with a roar each time, but a day + and it seems that the engine half starts and then it gets going after a second or two, Could it possibly be that the fuel injectors need to be cleaned with some of that additive in the gas tank? If so can anyone recommend a superior product? All help is greatly appreciated, Thanks in advance!