![[M54B22] High positive LTFT and negative STFT](https://preview.redd.it/wugsgx3cl91h1.png?width=140&height=36&auto=webp&s=064e00c7ec0afa823b275ce9f62ad75eb0ace6dc)
[M54B22] High positive LTFT and negative STFT
I’ve had a problem with my car for quite a while now. Something is causing:
- High idle RPMs (800–850)
- Higher fuel consumption
- Negative LTFT of around 14%, which triggers the check engine light
- Positive STFT at around 6–7%
All of this happens at warm idle. I know that most of these issues are interconnected (higher idle RPMs, higher-than-spec MAF readings, and increased fuel consumption).
Before I post the logs, here are a few things worth mentioning:
- The car was checked for vacuum leaks some time ago, and any leaks that were found were fixed.
- The MAF sensor is an original BMW OE unit, since Continental/Siemens sensors are no longer available. However, I’ll explain later why I don’t think the MAF is the problem.
- The idle is smooth despite the higher RPMs. It’s very stable and only fluctuates by around 15 RPMs. From my experience, vacuum leaks usually cause a rough and unstable idle.
- The car starts smoothly, even after sitting unused for a while.
Logs from warm idle:
I would ignore those two lowest points on the MAF and RPM graphs. As you can see, the MAF is steady at 3.15 g/s, which is higher than it should be, but the RPMs are also higher, so it could be that the engine is actually using that amount of air and the MAF sensor is not providing false data.
The O2 sensors concern me the most, since I have no experience diagnosing them, and both banks look quite different (e.g. a possible leak?).
If anyone has experience with O2 sensors, your feedback would be very welcome.
