First off, the correct DTC is P0300. Not 300. It is important to note the P and the four digits. All OBD-II codes are a letter followed by 4 digits.
It's possible wires are at fault depending on how many miles are on the car. I would check each wire for cuts and look at the part that goes down into the head..if it looks bubbled or burned it is cross-firing and that could be your entire problem. Crossfiring will result in a blackened sparkplug as well, pulling the plugs to assess their condition is a good idea. When was the last time you replaced them? Factory spec is every 30(maybe 36?) thousand miles. Get the bosch copper plugs for .99 each, they work fine. Make sure you apply a small amount of anti-sieze to the threads before you put the new ones in.
The other thing to check is the distributor, see if you have an oil leak coming from tbe bottom of the distributor housing. This is often times concealed because the oil hits the radiator hose and dribbles around rather than becoming a spot on the ground. The fix is to remove the distributor(MARK the position of the distributor relative to the head by scoring a line with a screwdriver or other tool BEFORE removal) and replace the o-ring. Mine turned hard and cracked, then started leaking around 57,000. While you're at it, remove the two 10mm bolts holding the cap in place and clean the cap and rotor if they show signs of contamination from the oil leak. Apply a small drop of blue loctite to the last few threads on the bolts for the cap prior to reinstallation to keep them from backing out.
Good luck with it.
Chris