Hyundai Repair: hyundai elantra gls 4 door 2000, hyundai elantra, secondary ignition

Question
they gave the following trouble codes #300 #301 #304 can you please tell me what they mean? thank you

Answer
These are all misfire codes.  P0300 indicates a random or multiple misfire; P0301 indicates a misfire on cylinder #1, and P0304 indicates a misfire on cylinder #4.  

The most frequent causes of misfires are the secondary ignition system components (plugs, wires, coil).  Check your plugs and wires first, but since the misfiring cylinders are both on the same coil pack, pay particular attention to the coil as well.