srdiserio

Need some help. Had an issue with the A3 shuddering under load...had the codes read and it was P0304 Cylinder 4 misfire (Ignition Coil) I replaced the Ignition Coil for #4 cylinder. I did end up getting the Durolast from AutoZone. It seemed to help at first, but looks like I am still having the same issue. Should I be replacing the spark plug as well? Should I buy the better ignition coil with plastic sheath? Any help I'd really appreciate. THANKS!