The coil pack (ignition coil) wiring harness wires are susceptible to cracking and degradation of the insulation covering the wires. This can result in misfires. Engine heat causes the wire insulation to crack and degrade.

The fix is to replace the wiring harness which is VERY time consuming. I did the work myself. The wiring harness itself is only about $30, but it takes at least 6 hours to remove the old wiring harness and replace it with the new one. It is very difficult to remove the pins of the old wiring harness from some of the connectors. The easiest way to deal with this is just to buy a new connector ($10) and then break the old one apart, remove the pins, and reassemble everything with the new connector.