Ok so I had a Service Engine Soon light for code P0300 and P0550. From all of the research i have done the P0300 can be multiple different things. I made sure that I had spark going to each cylinder before I started because it can be a coil pack. Most common are leaks in the intake system for example(the intake plenum gasket area is leaking, the pcv hose has a tear in it, etc,) basicly air is getting into your engine behind the MAF and Throttle body sensors.so it t means that extra air is getting into your engine that is not being monitored by the senosors. Therefore you get a random missfire because all the the cylinders are getting this extra air. On my car it was the pcv hose that was torn and all I had to do was replace it. Also make sure your exhasut gaskets around your catalitic converter are good and not leaking because it will cause the O2 sensors to not read the correct amount f exhaust because it is leaking out before the exhaust can get to the next o2 sensor. Once I change the hose to the pcv and my exhaust gaskets both codes went away after a short drive. This is just my exsperence with the p0300 code.