2003 Mountaineer. Change plugs and it stated running ruff at idle. Plain out then run ruff around55 mph. then plain off again. service light has been on for a year. had it read egr valve coil on #4 cylinder. Well replaced them. Lights still on and still runs ruff. Anyone have any ideas? It also said crank sensor. I thought it would cut out or not start at all if that was bad, Right?

 

You are right about the crank sensor, must have been a fluke malfunction that stored the code in the comp. If it started running rough after the plug change than maybe you might have messed up the firing order, mis- gapped plug or plugs, bad wire arcing or not fully plugged onto the spark plug, etc. Did you reset the computer after? Maybe a dirty IAC I think.

 

Is it always rough at 55mph? Maybe a faulty TPS(throttle pos. sensor) or VSS(vehicle speed sensor).