2003 Ford Crown Victoria 2003 Crown Vic Police Interceptor

Hello,

I have a 2003 Ford Crown Victoria Police Interceptor and my check engine light is on and the code reads cylinder # 2. I had all the spark plugs changed, all the boots changed, and I replaced coil # 2. And the light still came back on. Also when I am at a long traffic light the car starts to idle rough and if I am there long enough the car adjusts the idle and it is smooth again. But if I leave the stop light while it is idling rough the car miss fires but then will kick into full power a minute later. Otherwise the car runs fine. What do you think it could be? Also I drove it on the highway fairly fast (100mph) and when I got off the exit ramp, the light went off and stayed off for about 20 miles. Then it came back on. Thank you.