S40 Mixture Preparation Error

I'm at my wit's end! My 2009 Volvo S40 with a gasoline engine is throwing a 'mixture preparation error'. I've got reduced engine power, the check engine light is on, and it idles so rough it feels like it's going to shake itself apart. Plus, it jerks when accelerating and sometimes stalls completely. Honestly, could it get any worse? Has anyone else experienced this? Where should I even begin looking?

4 comment(s)

Sounds frustrating. The symptoms do point towards fuel delivery or air-fuel mixture issues. Have you checked the basics, like the air filter and throttle body? A clogged air filter can definitely mess with the air-fuel ratio. Also, any unusual noises from the fuel pump itself?

Thanks! I've checked the air filter – it's clean. Throttle body seems okay, no obvious gunk, but I haven't given it a proper clean. Fuel pump sounds normal to my ears. But could a faulty oxygen sensor cause these symptoms? I've read some conflicting info online.

Yes, a faulty oxygen sensor could definitely cause those symptoms. However, given the stalling and jerking, alongside the mixture error code, I'd be leaning more towards a fuel injection problem, particularly a defective injector. It's hard to say for sure without diagnostics. If you're not comfortable delving deeper yourself, it might be best to have a workshop take a look.

Thanks a lot for the insights. I took it to the shop, and you were spot on – a defective fuel injector was the culprit. Cost me 515€ to get it sorted, but at least it's running smoothly again. I really appreciate your help!

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