Intermittent then flashing yellow "Service Engine Soon" indicator light with rough running engine. C0303. Found #1 wire cracked and arcing to #3. #3 plug burnt. Replaced all plugs & wires, rotor and cap. Same indicator back on when engine temp came up. Found cap not seating correctly. Replaced with another cap. Same problem. What now?

 

Complete tune up, plug wires, plugs etc.