Could be a weak coil or bad ignition control module. The ICM can be tested at AutoZone. Just have them test it several times to warm it up. It could also be a bad valve or cam lobe. If it's fuel injected a bad injector.
could be distributor cap or rotor
Possibly a bad ignition coil or coil,bad timing, possibly a burnt out cylinder.
I would help to know what year and model vehicle you have but, you may have a bad fuel injector.
its a Nissan for starters but it could be the plug wires or the plugs or the distributor
you either did not gap the plugs to spec or you put this wires on wrong
Fuel injectors or coil
Start with distributor cap/rotor, spark plugs and spark plug wires.
if it has spark plugs check the distributor cap and/or rotor button for corrosion
I have a 95, had a misfire... mine was because of the plug wires... changed the wires and plugs mis fire stopped...
Last summer, the cylindars started to misfire on my 2002 lancer. Once the spark plugs were changed, I haven't had any more issues.
Bad plugs Wires, Distributor cap, Points if older model This is just a few things
There are a couple of reasons why a 1999 Ford Contour may misfire. The spark plugs may need changed or the coil pack may be bad.