I have a 03 ford ranger 3.0 V6. My check engine light often comes on for a few days then goes off for a few days then reappears. Every time it has been a cylinder 1 misfire. As soon as I start it up it idles rough and sputters some but if you let it sit for about 5 minutes or drive it on the highway nothing happens. It like it just goes away. I have replaced spark plugs, plug wires, and o2 sensors. I am curious to what it could be.