BMW 5 Series Diesel Power Loss & Stalling Mystery

Hey there! I had nearly identical issues with my 2005 BMW 330d (175k km). The symptoms you're describing match exactly what I experienced, rough idle, drop in power, and that annoying check engine light. My car would sometimes stall at traffic stops, which was really concerning. Got it checked at my regular garage last month, and yes, it was indeed a defective DISA unit. The valve was stuck and wasn't regulating the air intake properly. The mechanic showed me the old unit, the flap was barely moving and the vacuum lines were pretty worn out. They replaced the complete DISA unit, and the difference was night and day. The engine ran smooth again, idle stabilized, and power returned to normal. It's definitely not something you want to leave unattended as it can affect engine performance and potentially cause more serious issues down the line. For reference, a with similar problems tried fixing just the valve, but ended up having to replace the entire unit anyway, so I'd recommend going straight for the complete unit replacement.

Thanks for sharing that experience, it sounds spot on with what I'm dealing with! The car's behaving exactly as you described. Really helpful to know it was actually the DISA unit in your case. Just curious, would you mind sharing what you ended up paying for the repair? Also, has everything been running smoothly since the fix, or have you noticed any other quirks popping up? Thanks loads!

Hey again! Just wanted to update you, since my last message, I got the DISA unit replaced and it cost me 280 € for the complete job. Honestly, it was worth every penny. The car's been running like a dream, no more stalling at stops, no rough idle, and the engine's got its power back. Haven't had a single issue since the fix. It's funny looking back at how worried I was about the symptoms, but getting the complete DISA unit replaced was definitely the right call. My mechanic showed me the old unit afterward, it was in pretty rough shape! Seriously, if your symptoms match what I had, don't hesitate to get it sorted. It's not the cheapest repair, but it's way better than letting it cause more problems down the line. My 330d feels like a different car now, smooth, powerful, and running just like it should. Hope this helps with your decision making! Let me know how it goes if you get it fixed.

Thanks for the detailed update! I actually just got back from the mechanic today and wanted to share my experience. Unlike my last repair nightmare, this one went surprisingly well. Had the DISA unit replaced and you're right, what a difference! The mechanic spent time explaining everything and showed me my old unit. It was completely shot, way worse than I expected. Ended up paying slightly more than you, around 320 €, but honestly, it was worth it. The car's running beautifully now, no more stalling, idle's perfect, and that annoying check engine light is finally off. Funny thing, the mechanic mentioned he'd seen quite a few BMWs with the same issue lately. Guess it's a common problem with our models. Really glad I asked here first instead of trying cheaper fixes that probably wouldn't have worked. Thanks again for all your help. It's such a relief to have this sorted properly!