BMW Z4 Power Loss and Rough Running Mystery

Hey there! I had nearly identical issues with my 2012 BMW M3 last year. The symptoms you're describing match exactly what I experienced, power loss, rough idle, and terrible fuel economy. After diagnostic testing at the garage, it turned out one of my fuel injectors was defective and wasn't spraying fuel properly. This caused uneven fuel distribution and messed up the air-fuel mixture. It was indeed running rich, just as you suspect. This isn't something to ignore, a faulty injector can potentially damage your catalytic converter if left unchecked. In my case, they had to replace both the problematic injector and clean the fuel system. The car's been running smoothly since then, back to its normal performance and fuel consumption. Based on your symptoms and my experience, I'd strongly suggest getting those injectors checked ASAP. It's a fairly common issue with these engines at that age, regardless of the low mileage. Hope this helps!

Hey, thanks a lot for sharing your experience! This sounds exactly like what I'm dealing with. I've booked my Z4 for a checkup next week to have the injectors looked at. Just curious, do you remember roughly how much the repair set you back? Also, has everything been running smoothly since the fix, or have you noticed any other issues pop up? Would love to know what to expect. Cheers!

Hey again! Glad to give you an update! Got my injector fixed about 6 months ago and wow, what a difference! The repair cost me 515 €, yeah, not exactly cheap, but totally worth it. The mechanic replaced the faulty injector and did a thorough cleaning of the fuel system. My M3's running like a dream now, no more rich fuel mixture issues. The engine response is crisp, fuel economy's back to normal, and that annoying jerking during acceleration is completely gone. Haven't had a single problem since the fix, honestly. The car feels like new again! Just one tip, after the repair, I started using premium fuel and I think it's helped keep everything running smoothly. I know it costs a bit more, but I reckon it's cheaper than dealing with more injector problems down the line. Let me know how your repair goes next week! Based on your symptoms, I bet you'll notice a huge improvement like I did. Take care!

Thanks so much for all the detailed info! Just got back from the mechanic today, and you were spot on, it was indeed the injectors causing all the trouble. My repair bill came to around 500, pretty close to what you paid. The difference is incredible! Took it for a test drive after the fix, and it's like having a completely different car. The engine's running super smooth now, no more jerking or power loss. The mechanic also mentioned switching to premium fuel, just like you suggested. Really appreciate your help with this. Would've probably spent ages trying different fixes if you hadn't shared your experience. The mechanic even confirmed it's a common issue with these engines. They also did a full system cleaning while they were at it. Glad I got it sorted before it caused any more problems. Thanks again for pointing me in the right direction! Best regards!