I got a bunch of random misfire codes, P0300, P0301, P0302, P0303. and P0304. The car was sputtering a bit and jerky this morning, also got a big back fire when it shifted at 7K. Now I am letting the car cool off before I remove the plugs and check out the condition of them. At most I racked up 5K kilometers on the plugs so until I get a visual of the condition of the plugs what could this be?