It means the computer is detecting a misfire on those cylinders, the most common cause is worn spark plugs or spark plug wires. I would recomend replaces both then clear the computer codes and see if the service engine light comes back on.
Trouble code P0300 means:Random/multiple cylinders misfire detected
Cylinder number two misfire.
It means # 3 cylinder has a misfire. My advice is to replace all the spark plugs, and check the spark plug wires carefully.
Most of the time this means that the coil for that cylinder is bad. It can also mean a bad plug and sometimes the fuel injector.
Multiple or random cylinder misfire.
P0302 (M) Cylinder #2 Misfire Misfire detected in cylinder #2
A flashing check engine light is an indication of a misfire.
Cylinder #2 Misfire
That is a cylinder number eight misfire.
Cylinder number 3 misfire.
Cylinder number two misfire.
Cylinder #4 is misfiring in an engine with 4 or more cylinders. Engines have a firing order that is used to number the cylinders and it depends upon the engine which one is #4.