BMW 8 Series Multiple Engine & Exhaust Issues, Need Help

Hey there! I had similar symptoms on my 2019 BMW 7 series (also own a 3 series). I have some experience working on cars but nothing too advanced. The symptoms you described are exactly what I faced, rough running, CEL, poor performance, the works. Turned out to be a faulty lambda sensor. Got it fixed at my regular workshop, they diagnosed it quickly, replaced the sensor, and cleared the codes. Cost me around 375 Euro total. Before you jump to conclusions though, what's your exact engine variant and mileage? Would help to know if you're getting any specific error codes too. These symptoms can sometimes point to other exhaust system issues, so getting the right diagnosis is key. Hope this helps! Let me know the details and I might be able to share more specific insights.

Thanks for sharing your experience! My BMW just hit 122371 KM and had its latest service done 3 months ago. I'm getting error code P0420 which points to catalyst system efficiency below threshold. Your lambda sensor issue sounds similar to my symptoms. Did you notice any improvement in fuel consumption after the fix? I'm burning through fuel like crazy right now. I'll probably take it to a BMW specialist rather than my regular mechanic since the exhaust system seems pretty complex on these cars. Would be great if you could share which workshop you went to and if you're still happy with the repair job.

Hey again! Yeah, I totally understand your concern with that P0420 code. I had similar fuel consumption issues before the fix, was practically watching the fuel gauge drop in real time! After replacing the lambda sensor, I saw a massive improvement in fuel economy, probably around 15-20% better. The car felt much smoother too. Actually, my situation was pretty similar to yours, I was at about 115000 KM when these issues started. You're right about going to a specialist, I learned this the hard way. I first took it to my regular mechanic who couldn't properly diagnose it and wasted some time and money there. The repair has held up great so far, it's been about 8 months and no issues whatsoever. The car runs like new again. Just make sure whoever does the work clears all the codes properly and does a thorough check of the entire exhaust system while they're at it. My specialist also noticed a small exhaust leak at the manifold gasket which they fixed during the same visit. One thing though, since you're getting the P0420 specifically, they might want to check your catalytic converter too. Sometimes a bad lambda sensor can damage the cat if left too long. Might be worth having them inspect that while they're at it. Let me know how it goes with the specialist. Always good to compare notes on these things!

Thanks so much for all the detailed info! It's really helpful to hear your fuel consumption improved that much after the fix, gives me hope since I'm really tired of these frequent fuel station visits. Good point about the catalytic converter too, I hadn't thought about potential damage from running it too long with these issues. I'll definitely get that checked out when I take it in. You've convinced me about seeing a specialist right away instead of potentially wasting time and money elsewhere. When my regular mechanic saw me last week, he seemed a bit hesitant about diving into the exhaust system, so that was probably a red flag I should've noticed. I've already called a BMW specialist and booked it in for next week. They mentioned they'll do a complete diagnostic scan and exhaust system inspection first. Will definitely keep you posted on what they find and if it turns out to be the lambda sensor like in your case. Really appreciate you sharing your experience, it's given me a much better idea of what to expect!