BMW 5 Series Diesel Power Loss & Rough Running Issues

I had a similar issue with my 2012 BMW 3 series diesel. I have some basic experience working on cars, mainly routine maintenance stuff. The symptoms you're describing sound exactly like what I dealt with. My car was doing the same, sluggish performance, rough idle, and drinking fuel like crazy. Turned out to be a faulty vacuum switching valve. Got it fixed at my regular workshop for about 140 Euro, which included parts and labor. The repair took around 2 hours. Could you share your exact engine variant and mileage? This could help narrow down if it's the same issue, as these problems can be pretty common on certain BMW diesel engines. Before you head to the shop, have you had the error codes read? That'd be really helpful to confirm if we're dealing with the same problem here.

Thanks for sharing your experience! My car has 108840 KM on the clock, and I just had it serviced last month. I'll definitely get those error codes checked out. The vacuum switching valve issue you mentioned sounds pretty spot-on with what I'm experiencing. Did you notice any other warning lights besides the engine light when you had this problem? Also, was your car hesitating specifically during acceleration like mine? I'm trying to figure out if I should expect a similar repair cost and timeframe.

Hey again! Yeah, when I had this issue on my 3 series, I definitely had the check engine light on, plus the reduced power warning that would pop up intermittently. And yes, the hesitation during acceleration was super noticeable, it felt like the car was surging forward in waves, which was really annoying. Since you mentioned your recent service, it's worth noting that my problem started about two months after a regular service too. I initially thought it might have been related to the service somehow, but it turned out to be just a coincidence. The vacuum switching valve just tends to fail around this mileage range. Your mileage is pretty close to what mine was when I had the issue (mine was around 115000 KM), so it's looking even more likely that we're dealing with the same problem. The repair cost I mentioned earlier should be pretty similar for you too, though prices might have changed a bit since I had mine fixed. One thing I forgot to mention in my first reply, after the repair, I noticed an immediate improvement in fuel consumption. The car went back to its normal fuel efficiency within the first tank. If you do get it fixed, you should notice the difference right away too.

Thanks so much for all this detailed info! It's really helpful to hear about your experience with such similar symptoms, especially since our mileages are so close. I feel much more confident now about what I might be dealing with. The surging forward in waves you described is exactly what I'm experiencing, it's like the car can't decide if it wants to go or not. I'm actually relieved to hear it might just be the vacuum switching valve. I was worried it could be something way more expensive! I'll get those error codes read tomorrow and have my mechanic check specifically for this issue. The repair cost and timeframe you mentioned sounds totally reasonable, and honestly, I can't wait to get back to normal fuel consumption. Really appreciate you taking the time to share all this. It's super helpful going to the mechanic with some actual knowledge about what might be wrong instead of just saying "it's acting weird!"