BMW Z3 Stalling at Idle: Bad Fuel or Hidden Issue?

Hey there! I've got some experience working with BMWs as a hobby mechanic. Had a similar issue with my 2004 BMW Z4 last summer, and my owns an M3. The symptoms you're describing sound really familiar, my car was stalling at idle too. Turned out it was a loose connection in the wiring harness near the fuel pump. Took it to my regular workshop, and they diagnosed it pretty quickly. Total repair cost was around 95 Euro, mainly labor for tracking down and fixing the faulty connection. Before jumping to conclusions though, could you share: What error codes are you getting? Does it happen more when the engine is cold or warm? Any recent fuel fills from different stations? This info would help narrow down if you're dealing with the same issue I had or something else. These older BMWs can be tricky, but they're great cars when running right!

Thanks for sharing your experience! My Z3 currently has 135357 KM on the clock. The stalling mostly happens when the engine is warm, especially after my latest service. I'm getting P0171 and P0174 codes, which point to a lean condition. I've been using the same fuel station consistently, but recently they were doing some tank maintenance, so that got me thinking about potential contaminated fuel. The car runs fine at higher RPMs, it's just the idle that's problematic. Maybe I should try running some fuel system cleaner through it first before diving deeper into potential wiring issues? Would be great to avoid an expensive repair if it's just bad gas.

Hey again! Thanks for those details about your Z3. Actually, when I had similar issues with my Z4, I first thought it was contaminated fuel too, but running fuel system cleaner didn't solve it for me. Those P0171 and P0174 codes you're getting, they're exactly what I saw before finding out about my wiring issue. The lean condition can definitely be tricky to diagnose. While my problem turned out to be the wiring harness, I did try the fuel system cleaner route first, just like you're thinking. Spent about 15 bucks on premium cleaner, but sadly it didn't help much. Since you mentioned it's happening after your recent service, might be worth checking if anything got disturbed during the work. In my case, the loose connection was actually near where they had been working during a routine service. Tell you what, before you spend money on cleaners, maybe check the MAF sensor and vacuum lines? These are common culprits for lean conditions in these engines, and they're easy to inspect yourself. My 's M3 had similar symptoms from a cracked vacuum line, and that was a super cheap fix. If you want, I can share some specific spots to check for vacuum leaks on these engines, I've become pretty familiar with them after all my troubleshooting adventures!

Thanks for the detailed response! I really appreciate you sharing your experiences with both your Z4 and your 's M3. You've given me some solid points to look into. I think I'll skip the fuel system cleaner for now and follow your advice about checking the MAF sensor and vacuum lines first. It makes a lot of sense that something might have been disturbed during the service. Would definitely appreciate any tips about specific spots to check for vacuum leaks! I'm fairly handy with tools and would love to at least inspect these areas myself before taking it to the shop. Hopefully it'll turn out to be something simple like your 's cracked vacuum line rather than a wiring harness issue. I'll let you know what I find after checking those spots. Thanks again for taking the time to help out, this is exactly the kind of firsthand experience I was hoping to hear about!