Consistently Negative LTFT Interpretation

I would like to check what could be wrong if GTI has been reading consistently negative LTFTs. Here are the key info:

1. 8 year old stock GTI, no tune or hardware modifications except a CTS intake.
2. Using OBDEleven to read data.
3. LTFT is at -10 to -14%.
4. STFT is at 0 to +3% at idle, but fluctuates up to -10 to -14% under load 1.5k RPM to 3k RPM.
5. MAF at idle is reading ~3 to 6 g/s. At WOT it goes up to 220 g/s.
6. O2 sensor voltage is ~6 to 7 volts.
7. No boost leaks (as far as I can tell. No obvious signs of power loss throughout the RPM range).
8. MAF cleaned with contact cleaner.
9. No visible signs of fuel injector leaks (no gas smells, etc).
10. Have yet to physically remove the injectors or spark plugs to inspect them.

A few days ago LTFT was at -14%, just today a random CEL came up reporting MAF error and after I cleared it LTFT was reset and began to settle around -10%.

Should I be concerned that there’s something going on or is this normal? I’ve done a bit of research and some people have commented that it’s normal for trim levels to vary more with age.


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I'd run logs to check for boost leak and then do an actual boost leak test with a compressor

Upon further observation, I’ve noticed that the Bank 1 Sensor 2 voltage is erratic and not behaving as how it should be. Perhaps the O2 Sensor is on the way out!

At idle, the voltage hovers between 6v to 7v.

At highway cruise (2-2.5k RPM), sometimes it fluctuates between 4v to 6v. This is supposedly normal behaviour. But, the majority of the time it stays between 6v to 7v. When I let off the gas while cruising, it drops to 0v and doesn’t move until I give a little bit of gas before it shows about 1v to 3v.

Anyone have any inputs on this kind of O2 Sensor behaviour?


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did you ever fix this?