Hi, I'm new to the forum and need some advice. I have a 2006 Impreza WRX and recently replaced all the coil packs after it was diagnosed that one of the cylinders was misfiring (decided to just change out everything). It still misfires but not all the time. If it misfires I'll shut the engine off, restart, seems okay then. It misfired this morning and it was a fairly cold morning. The "check engine" light doesn't light up, either.

Any insight as to why this is happening? Fuel injector issues? Thanks.