This actually started a few months ago after driving through some puddles just after a heavy rain. Would idle just fine and drive at low rpm (under 4k)just fine. If I get into the throttle it will misfire at about 4,000 - 5,000 rpms. wrote it off as a coil getting wet or something related to moisture. Now it does it even when it is dry and throws the P0300 code. This appears to be one of those somewhat generic codes that could be one of 20 things causing a random misfire! Any suggestions where to start? I replaced LIM gaskets a year ago, plugs and PCV valve at that time too.