Have code po306 cylinder 6 misfire detected. What should I look for bad plug
on 1998 Mercury Villager

Seems to be running on 5 cylinder when under lug but runs fine some of the other times. Starts and idles fine.

2 answers
yes i changed knock sensor lower intake gasket upper intake gasket added antifreeze also changed injector rings still runs rough and doesn/t stay on steady shuts off
Have compression checked if ok a GOOD tune up may be in order.