One of the more common P0300 random misfire code causes is a leaking valve cover gasket. A leaking valve cover gasket allows the spark plug wells to fill with oil and randomly short out the spark plugs. Pull a plug wire at the plug and look down the hole at the plug and check for oil. Check all the plugs this way and if oil is present you will need 4 new plugs, a plug wire set, and a valve cover gasket set to put the car right. If no oil is present, pull each spark plug and inspect the electrodes for condition and gap - excessive gap can cause a misfire. If the gap is excessive, time for new plugs. If the gap is good, check the insulator for carbon tracking. If carbon tracking is present, replace the plugs and the wires. If all checks out, the coil packs are the next suspect. I hope this helps.