Fiesta Rich Mixture Rough Running

I had something similar happen with my Fiesta! Reduced power, rough running, and the check engine light sound familiar. A 'rich mixture' means there's too much fuel compared to air in the engine. The mechanic is right, faulty fuel injectors could definitely be the culprit. But before you jump to replacing all of them, have you checked your air filter recently? A clogged air filter can restrict airflow and cause a rich mixture too. Also, have you had any issues with your catalytic converter? I had to replace mine, too, when I had all those symptoms, maybe ask him to take a look.

I did check the air filter, and it seemed okay. The catalytic converter is an interesting point, though. What kind of issues were you having with your catalytic converter, and how did you know it was failing? Also, were your symptoms constant, or did they come and go? Trying to give the mechanic as much info as possible before he rips apart my engine. Also, did you manage to fix your rough idle in the end?

Okay, so if the air filter is clean, it probably is the injectors or catalytic converter. The symptoms were pretty consistent, rough running, check engine light, and it got worse over time. Eventually, the car started failing emissions tests. The rich mixture can damage the catalytic converter. Honestly, at this point, I'd probably trust your mechanic to diagnose it properly with their equipment. They can test the fuel injectors and check the catalytic converter's efficiency. That´s what I did, anyway!

Thanks so much for sharing your experience! I really appreciate the advice. I took it back to the mechanic, and after a thorough check, it turned out to be a defective fuel injector, just as he suspected. I had all four replaced. The final bill came to 515€, but the car is running smoothly again. No more jerking or rough idling. Hopefully, this thread will help someone else facing a similar issue in the future!