89 formula tpi all stock 305. just started missing slightly. When I first start in the morning motor runs perfect for about 1/2 mile then starts skipping. Could this be an injector? No codes set. I figure in open loop (when cold) it's supplying enough fuel , but when in closed loop it's not enought fuel. Am I on the right track? Just changed plugs cap rotor wires oxygen sensor. 125k miles on car. Thanks all----------