Z4 Knock Sensor Drama: Stalling, Sluggish, Thirsty Engine

Hi there! I own a 2007 BMW Z4 3.0si and had almost identical symptoms last year. The sluggish performance and rough idle definitely rings a bell. In my case, it turned out to be a damaged wiring harness connecting to the knock sensor, not the sensor itself. The mechanic found that some wires had worn out due to engine vibration and were making intermittent contact. The connector was also corroded. The fix involved replacing the wiring harness section and the connector plug. While diagnosing, they also found the O2 sensor was showing early signs of failure, which explained the increased fuel consumption. This wasn't a major repair in terms of complexity, but if left unchecked it could have led to serious engine damage from incorrect timing adjustments. Everything's been running smoothly since the repair. Don't wait too long to get it checked, these symptoms usually don't fix themselves and can get worse. Make sure they properly check the wiring and connections before just swapping out the sensor.

Thanks so much for sharing your experience! That's really helpful info about the wiring harness, definitely sounds similar to what I'm experiencing. Would you mind telling me how much the repair ended up costing you? And has everything been running perfectly since, or have you noticed any other issues pop up? I'm trying to budget for the repair and want to make sure I'm prepared for any potential related problems.

Hey again! Good news, I got it all sorted out! Took your advice and had a proper mechanic check it thoroughly. You were spot on about the wiring, turned out it was just a bad cable connection to the knock sensor causing all the drama. Only set me back 95 € to fix, which was way less than I was worried about. And what a difference! The car's running like a dream now, no more sluggish acceleration or rough idling. That fuel consumption's back to normal too. It's been several months since the repair and haven't had a single problem. Really glad I didn't just ignore it and let it get worse. Just shows sometimes it's the simple things, right? No need for any other repairs either, once they fixed that dodgy connection, everything else fell right back into place. Total relief it wasn't anything more serious! Let me know if you need any other info about it.

What a relief to hear back! I actually just got my car back from the shop yesterday. You were right about getting it checked quickly, I found a reputable BMW specialist who did a thorough diagnostic. Funny enough, my issue was slightly different from yours but still pretty straightforward. Turned out to be a combination of a dirty MAF sensor and a small vacuum leak. The whole thing cost me about €250 including parts and labor, which wasn't nearly as bad as I'd feared. They cleaned the MAF sensor and replaced a cracked vacuum hose. The car's running like new now, that sluggish feeling is completely gone, and my fuel economy has improved dramatically. I'm really glad I reached out here. Your experience helped me feel more confident about getting it checked, and now I've found a mechanic I can trust. Thanks again for sharing your story, it really helped me make the right decision instead of putting it off and potentially causing more damage.