OK so cruising along today in my mostly stock gst. All of a sudde. It lost all power. The tach started going crazy, the idle dropped to a near stall. I cut the car off. Sat for about 15 minutes. Started the car up runs perfect. Drive about 10 minutes and does it again. I get it to my dads and pull the plugs. 3 were a light grey color. The 4th was black and looked burnt. I suspect fouled plugbut why does it idle fine and then lose power. Also the motor shakes violently. Is the coil packs on their way out or just a fouled plug?? Please any help. Thanks