BMW Z3 Knock Sensor Issues? Troubleshooting Guide Inside

Hey there! I have some experience working on BMWs. I dealt with very similar issues on my 2002 BMW 330i (also had a 325i before). The symptoms you describe sound really familiar. My car had the exact same problems, check engine light, bad fuel economy, and that annoying rough idle. My mechanic diagnosed it as a faulty knock sensor connection. The actual sensor was fine, but the wiring and plug were corroded. Got it fixed for around 95 Euro and all those issues disappeared completely. Before I can help more specifically, could you share: Have you scanned for error codes? Is the check engine light solid or flashing? Any other warning lights on? The repair was pretty straightforward in my case, but knowing these details about your Z3 would help determine if you're dealing with the same issue.

Thanks for sharing your experience! Just had my service done at 112649 KM, and yeah, I've been dealing with these exact symptoms. I picked up an OBD scanner and got error code P0325, which points to the knock sensor. The check engine light is solid, no other warning lights. The sluggish response and fuel consumption are really becoming a pain. Definitely sounds like I'm dealing with what you had. Really hoping it's just the wiring/connection like in your case, that would be a much cheaper fix than replacing the whole sensor. Did you notice any improvement in performance right after the repair?

Hey again! Glad you got those codes checked. Yeah, P0325 is exactly what I had on my 330i. And yes, the performance improvement after fixing the wiring was like night and day! The sluggish response disappeared completely, and my fuel consumption went back to normal within the first tank after the repair. I totally get your pain with those symptoms, it's super frustrating. In my case, once we cleaned up the corroded connections and replaced the wiring harness, the car felt like new again. The rough idle smoothed out immediately, and the engine response became much crisper. The repair took about an hour, and like I mentioned before, cost me around 95 Euro. Quick tip from my experience, while you're in there, it's worth checking the surrounding wiring too. These BMWs can develop corrosion in other nearby connections, and since you're already going to have that area exposed, might as well give everything a good look. Just make sure whoever does the repair checks the wiring first before replacing the whole sensor. Would hate to see you spend money on a new sensor if it's just a connection issue like mine was. Keep me posted on how it goes!

Thanks so much for the detailed advice! That's really encouraging to hear about the immediate improvement you saw. I've actually got an appointment scheduled with my mechanic next week. I'll definitely have them check the wiring and connections first before jumping straight to replacing the sensor, could save me a bunch of money. Really appreciate the tip about checking the surrounding wiring too, makes total sense while everything's already opened up. It's such a relief to hear from someone who dealt with the exact same issue and got it sorted. I can't wait to get my Z3 running properly again. Will definitely update you once it's fixed. My mechanic quoted me similar costs to what you paid, so fingers crossed it's just the wiring. Thanks again for all your help!