Sometimes when I turn my car off and then restart it (ie. at a gas station etc.), when I go leave and step on the gas a little hard it stumbles and does a little backfire and feels really restricted. I ease off a little bit and then I can feel it wanting to go again...I step on the gas and it goes like a rocket!! Why is it doing this? It did it even before my mods. Is this some sort of computer safety feature or something?