Hello, I'm having a bit of an issue with my Saab 9-3. Whenever I get on boost in fourth or fifth gear, my engine shudders a decent bit, feels like a misfire. I also got the P1312 code, which pointed to either the plugs or coils being bad. I had previously replaced one of the ignition coils when it failed a few months ago, and replaced another one today with one from Standard Motors, part number being UF526. I know that Intermotor ignition coils are considered to be good replacements, and I believe that Standard Motors owns Intermotor. I do not believe the issue is from the ignition coils, but rather the spark plugs. When I pulled the spark plugs out to properly gap and clean them, I noticed one of them has a hairline crack in it. Would the issue be caused by the cracked spark plug? I'm hoping it is. Also, what is a good way to test ignition coils, just to make sure the other two are not on their way out.