Seat Altea running rich

I had a similar issue with my Seat Leon. Symptoms were very similar: rough idle, poor fuel economy, and the engine management light illuminated. The diagnostic codes pointed to a rich mixture. Have you checked your oxygen sensor? A faulty sensor can cause the engine to overfuel. Also, are you experiencing any jerking during acceleration?

Thanks for the quick response. I haven't specifically checked the oxygen sensor, but the error codes I pulled mentioned potential issues with the injection system. Did your Leon also have problems with the catalytic converter due to the rich mixture?

Yes, the rich mixture did eventually cause problems with the catalytic converter on my Leon. It wasn't immediately apparent, but the prolonged overfuelling damaged it over time. Given your symptoms and the error codes you're seeing, it's highly probable that you have a faulty injector. If you lack the specialist tools and diagnostic software, I would recommend a professional workshop assessment to confirm and rectify the issue.

Took the Altea to the workshop. Injector number 3 was faulty. A new injector was fitted, plus new spark plugs since they were fouled. It's running smoothly now, and the check engine light is off. Total cost 515€.