[12Ounce]

I reads as though you are getting an intermittent miss-fire. I would pull the plugs and inspect to see if any show oil or other indications of miss-fire. While the plugs are out I would conduct a compression test to see if any valve-burning is evident.

If the compression on all cyls is "even" ... I would be suspicious of some spark issue. The coil, the crank pos sensor, the cam pos sensor, etc, etc...