Misfire, #6
You should probably start with removing the spark plug and just replacing it if you don't have the means to test it (i.e. color, cracking insulator etc.) Next would be the ignition coil(s); probably have to switch or replace for any confirmation. It could also be the air/fuel mixture sensor, Oxygen sensor (s), EGR valve, the catalytic converter, leaking air hose after the air/fuel sensor etc. If it runs fine, get a OBDII checker that can graph oxygen sensor status (~$50 for one that can do this).
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