Ford Focus Mixture Preparation Error

I had something similar on my Focus. Same symptoms – rough running, check engine light. I was chasing my tail trying to figure it out. Did you check the mass airflow (MAF) sensor? A faulty reading can throw off the air-fuel ratio, leading to a rich mixture. Also, how's your catalytic converter and oxygen sensor looking? They play a big part in regulating that mixture too.

I haven't really checked the MAF or oxygen sensor. When your Focus had these symptoms, did you see any specific diagnostic codes that align with my 'mixture preparation error'? Was the issue constant, or intermittent? I want to avoid replacing functional components if I can.

Yes, it sounds awfully familiar. It was indeed the injection valve which was defective. My mechanic mentioned the catalytic converter working harder to compensate for the rich mixture, which isn't ideal. Honestly, I'd suggest taking it to a trusted workshop, as pinpointing the exact faulty injector without proper equipment can be a headache. I paid around 515€ for the repair.

Aha! Your experience resonates. The confirmation about the injection valve is what I was looking for. Thanks for your insights. I'll have the injectors inspected and replaced if needed. Your guidance has saved me time and potential expense. Thanks!