My son brought the car home and said it was running rough. I put the reader on and got P0303,P0304,P1399. I cleared the codes to reset and just got the second two after about 4 minutes of idleing from a cold engine. Although the engine was running rough I didn't get the engine light for 4 minutes. I changed plugs cap rotor checked the resistance of the wires and of the coil. Found the secondary winding to be out of limits but when I went to the parts store for a new coil the readings were the same as the old one. The compression was good on all the cylinders and didn't leak down. Pulled the plugs after 15 minutes of driving all look brand new except no. 4. Please offer any help. Thanks

 

I swapped wires and the code followed, even though the resistance check was ok on the wires it turned out to be a bad wire. Changed the wires and all ok

 

Nice trouble shooting.
With the high voltage threw the plug wires they must be breaking down under a load. Out of curiosity what were the readings