2002 2.2l sunfire misfire P0300

The other day I started my car and noticed a lot of exhaust was coming out of the muffler, so when I starte to drive the car wouldn’t go faster then 40k and the revs went up and the engine light started flashing !
We plugge in the code reader and said misfire cyl 3
We changed all the spark plugs and two were soaked with oil
Changed the coil pack an still does the same !
I just want to know what the problem is

Possible causes