2001 Ford Focus ruff idle and backfire

The car will run fine but sometimes when I start it the car runs like it out of time. I can disconect the wire from the coil for a minute and it will start fine but when i turn it off and start it again, it does the same thing. I have replaced the plugs, wires and coil but still does the same thing. Could the new coil be bad also, or should I try something else ?
Thanks, C J