SOme times when i start my car it will back fire when i give it gas...when i am driving down the street keeping speed same...car acts like its running out of gas, like its choking, then when i step on it, it will chug chug then start to move. Back fires alot to when i do this. Is the a problem due to back exhuast leak or dirty fuel filter, pump,? What can i do.....I thought it was the injectors...so i put concentrated injector cleaner in the gas adn it seemed to run alittle better but not for long. it could all be in my head.. any one know what is wrong?