1998 Chevy Astro 98 Chevy Astro

I have a 1998 chev. Astro that has a problem starting when it is very cold out. It tends to flood and will not start at all. Or it starts and runs rough. The engine check light is on, had it checked, and it coded engine missing. I can drive it but it is using excessive amount of gas.I have changed plugs, plug wires, cap, and roter. When changing plugs, I found that number 4 cylindar spark plug was kind of dark; Like it hasn't been running clean. Does this sound like I have a fuel injector stuck open on number 4? And if so can I just change just the one injector?