Crown Victoria rough engine cylinder misfire

Rough engine and check engine light, huh? Sounds familiar. Cylinder misfire, you say? Did you check the error code? It usually tells you which cylinder is acting up. How old are your spark plugs? Old plugs can definitely cause misfires. Is it just rough at idle, or does it get worse when you accelerate? What kind of fuel are you using?

I don't know the error code, haven't checked it. Spark plugs haven't been changed recently. The engine runs rough at idle, and it gets worse when accelerating. I'm using regular gasoline.

Regular gasoline should be fine. If it's rough at idle and gets worse when you accelerate, and you haven't changed the plugs in a while, that's suspect. But if the check engine light is on and you are seeing error codes related to combustion misfires, the problem is probably related to the injection valve/injector of the affected cylinder. Honestly, sounds like you should get it to a workshop. They'll be able to diagnose the exact cause and fix it properly. Agree?

Took the car to a workshop as suggested. Diagnosis confirmed a defective fuel injector, and the repair cost 515€. The car runs smoothly again now. Thanks for pointing me in the right direction.