When was the last time the plugs and wires were changed? A good way to tell if you have some bad wires is to pop the hood and fire it up in complete darkness and mist the plug wires with water. If you see any white or blue spark jumping to a ground (engine block, dogbone, etc) then you have bad wires. If you change the plugs only use the stock irridiums or a copper plug. These ignition systems do not use Platinum plugs.