We have a 2004 Mountaineer, and at 44K , we experienced a sudden problem with a rough running engine, accompanied by the check engine light. We thought that it might be bad gas, but ut did not go away. Turned out to be a bad fuel injector, or that is what the dealer said. Runs fine now, but have not heard of this being a problem.

 

Sometimes an injector will go and mispulse or get a little clogged up so it cannot emit the fine mist it was designed to. That would cause power loss and rough idle by being down a cylinder..