BMW X3 Diesel: Cold Start and Power Loss Mystery

Hey there! I've got some experience with BMWs as I faced something very similar with my 2006 BMW X5 Diesel. Had the exact same symptoms you're describing. Turned out my issue was linked to a previous repair job where they messed up the timing belt replacement. The workshop fixed it free of charge since it was their mistake. The symptoms were spot-on with what you're describing, rough cold starts, high fuel consumption, and lack of power. I've worked on basic car maintenance myself but always leave the complex stuff to pros. I'd suggest getting a diagnostic scan first, could be related to fuel injection timing or compression issues. Have you noticed any blue smoke from the exhaust? Also, when was your last major service? BTW, I also owned a 3 Series from the same era, and these symptoms can mean different things across BMW models. Could you share your mileage and service history? Might help narrow things down.

Thanks for sharing your experience! My last service was just 3 months ago at 138003 KM. Haven't noticed any blue smoke actually, but the fuel consumption has definitely gone up in the past few weeks. The symptoms started gradually, not suddenly like yours. You mentioning the timing belt got me thinking, during my last service they did check the timing belt but said it was still good. Maybe worth having another look at it though. The diagnostic scan sounds like a good first step before jumping to major repairs. Have you or anyone else experienced these issues being related to the fuel injectors? Been reading up a bit and it seems like that could be another possibility.

Hey again! Yeah, after reading about your gradual symptom onset, I'm actually thinking it might not be the timing belt like in my case. The fact that yours started slowly makes me lean more towards fuel injectors, which is what I was initially suspecting with my X5 before we found the timing belt issue. Actually, had a similar gradual power loss and rough starting in my old 3 Series, and it turned out to be gunked-up injectors. The symptoms started just like yours, creeping up over time rather than suddenly showing up. Plus, with similar mileage too. The no blue smoke thing is actually good news, means your engine isn't burning oil at least. In my experience, when these diesel engines start having injection problems, you'll notice the roughness more in cold weather first, then it gets progressively worse. Quick tip from my experience, before going for a full injector replacement, try running a couple of tanks with good quality diesel and a proper fuel system cleaner. Sometimes that's enough to sort it out if caught early. Worked for me once, but obviously won't help if the injectors are actually worn out. By the way, how's the engine sound when idling? Any rattling or diesel knock that's louder than usual? That could help confirm if we're on the right track with the injector theory.

Thanks for all the detailed info! The engine does have a bit more of a rattle at idle than usual, especially when cold. I'll definitely try your suggestion about the fuel system cleaner first, seems like a smart move before diving into expensive repairs. I just filled up with premium diesel and got a highly-rated injector cleaner from the auto parts store. Going to run that through for a couple of tanks like you suggested and see if it makes any difference. The gradual onset of my issues does sound very similar to what you experienced with your 3 Series. Really appreciate everyone taking the time to share their experiences. I'll keep an eye on the idle sound and overall performance with the cleaner treatment. If that doesn't help, at least I know to have them check the injectors when I take it in. Will update once I know more in case it helps someone else with similar issues later on.