Start the motor. Then when it starts missing start pulling off plug wires. If it boggs down the motor then put that wire back on. Keep going till you get to one that dont effect the idel dont change when its unpluged. That cylinder isnt firing. Put a new plug in the cylinder that is not firing. Then also put a plug wire that you know is good. Iv had plugs that would just stop firing for some reason.

It could also be a cloged injector.

Does the motor smoke when it misses? I had a missing problem and it only smoked when it missed. I tried different plugs and wires and it ended up being the head gasket was leaking just a little bit. The little that it was leaking it burnt and then smoked. the antifrez never got into the oil.