BMW Z3 Rough Idle and Stalling, Common Causes Revealed

Hey there! I experienced nearly identical issues with my 2004 BMW Z4 (gasoline) after changing the fuel filter. The symptoms you're describing match what I went through, rough idle, stalling, weak acceleration, and that dreaded check engine light. Took it to the garage, turned out the fuel pressure regulator wasn't the culprit. The main issue was actually a faulty Mass Air Flow sensor combined with a vacuum leak near the intake manifold. The mechanic mentioned this is fairly common in these models after filter changes if everything isn't sealed back properly. Not a catastrophic problem, but definitely needed professional attention. The fix involved replacing the MAF sensor and resealing the vacuum lines. Car has been running smooth since then, no more stalling or power issues. I'd recommend getting it properly diagnosed rather than just replacing parts hoping to fix it. These symptoms can be tricky to pinpoint without the right diagnostic tools. Good luck with the repair.

Thanks for sharing your experience. Really helpful to know about the MAF sensor and vacuum leak situation. My symptoms do sound pretty similar to what you went through. If you don't mind me asking, do you remember roughly how much you ended up paying for the whole repair? Also, has everything been running smoothly since then, or have you noticed any other issues pop up?

Hey again! Actually, turns out I was wrong in my first reply, in my case, it really WAS the fuel pressure regulator that was acting up! Got it sorted at the mechanic's and the car's running like a dream now. After they fixed the faulty regulator and cleared the error code from changing the fuel filter, it only set me back 45 bucks. Pretty reasonable, if you ask me! The throttle response is way better now, no more stalling or rough idling issues. It's been about 3 months since the fix, and honestly, my Z4 feels as peppy as ever. Haven't had a single problem since then, runs smooth as silk and the engine light has stayed off. Funny how I initially thought it was the MAF sensor and vacuum lines, but sometimes the obvious answer is the right one! Definitely glad I got it properly checked out though. These BMWs can be tricky to diagnose without the right tools. Hope this helps clarify things! Let me know if you end up getting yours fixed, would be interesting to hear if it's the same issue.

Thanks for the follow-up! I actually just got back from the mechanic today and wanted to share what happened. After seeing your message, I decided to bite the bullet and take it in. Turns out my issue was a combination of problems, clogged fuel injectors and a weak fuel pump. The mechanic showed me the dirty injectors, which explained the rough idle and power loss. Total bill came to about €400, including parts and labor. The difference is like night and day! The engine purrs now, and that annoying stalling problem is completely gone. Really glad I didn't try fixing it myself. The mechanic was super professional and walked me through everything they did. Even showed me the old parts and explained what went wrong. Funny how we both had fuel system issues, just different components! Thanks again for encouraging me to get it properly checked out. Now I can finally enjoy driving my Z3 again without worrying about it dying at every stoplight.