HELP! Truck Started Running Rough This Morning

Ok, today I started by truck up and it runs rough. And my engine light comes on. I went by auto zone and there code scanner doesn't come up with anything. There is a sweet spot at like 50 or so, and it will run normal. I am going to swing by advance in a bit and see if there scanner comes up with anything. I have read a little about the connector under the valve cover coming loose. Were should I start first. I need to get it running right asap, as it is my daily driver. Oh and its a 02 f250 with the 7.3l.