Seen this problem quite a few times. It is in the Ignition coil pack's wiring harness. Remove Black plastic cover over Valve cover to gain access to the Coil Pack's. You will probally need to remove the air intake pipe & reinstall it. With the engine running wiggle & move the fat foamed insullation of the wires leading to the coil pack's (don't worry) You won't get shocked. Doing this will probablly mimic the problem. Sollution Repair damaged wiring for coil pack's by replacing harness or have it rewired by a skilled tech.
Good Luck !