Ok so I have replaced the entire exhaust, egr valve, tps, spark plugs and wires twice, cap and rotor, fuel filter, head gasket, fuel injectors, everything I could think of and yet EVERY time I stop at a stop sign or red light, and occasionally whenever I am going under 40, as I go to slowly press in the gas it will hesitate. Only for like 30 seconds to a min depending on its mood. My rpms will jump and slowly decline, until I press the gas petal almost to the floor and it snaps out of it, I recently discovered that it is backfiring towards the end of the hesitation and blowing dark grey smoke. Also now when I push the petal down to get it going my transmission acts like it has kicked into neutral and my rpms will rise but my car will not move. Help please

 

unplug the oxygen sensor and drive around and see if the issue subsides..if it does the problem is oxygen sensor related