low idling, stalling and black smoke. on 2002 Jeep Liberty

I drove my vehicle down from MD and had no problems. I made it into FL and filled up at a BP pump with 10% ethanol. I drove about 15-20 miles down the road and my car stalled and died. I can start it and it runs but I have to keep my foot on the gas so it doesn't stall. I took it to autozone and they ran the diagnostic, saying the coil pack was bad on one spark plug and one spark plug needed to be changed. I put fuel injector in it, changed the coil pack and the spark plug. it's still idling really low and smoking. Does it need new fuel injectors, fuel filter or broken valve spring? I'm not sure what I should try first?

Asked by for the 2002 Jeep Liberty