I had one stuffed coil pack and it made my car miss fire intermittently. One spark plug looked a little different in the fouling. Because it was only sometimes it had not changed the plugs appearance a lot. I changed all coil packs as my car has done 185000km and I just bought it so I don't know when they were last changed. Either they have done a great amount of KMs or they have been changed once before as they normally last about 100000km.