I got several codes indicating cylinder misfires. Engine running very rough. Turned engine off and back on and engines ran smooth but check engine remained on. Dealer said all spark plug way out of spec. (121K miles on car). Did the same thing after all plugs replaced. Tech advised of perhaps a deeper problem (cylinder 4 problem). The fact that when I restart the car it runs fine, gives me a feeling perhaps the problem is something electrical, like a sensor and not a mechanical issue. Any ideas?