Shorted coilpack

That is strange. The fact that it runs good until it shorts out makes me think the PCM is doing its job. I know that if the plug wires have too high of resistance, that can fry a coil pack.
I would probably replace the plugs and wires if it was my car. They also call to apply Silicone Dielectric Compound to all ignition wire boots, and make sure they are fully seated. Check under the coil pack and make sure it is clean and dry. The silicone can be applied under the coil pack also. If these things dont correct the problem, I would suspect the PCM, although that is highly unlikely.