My vehicle (Ford Fiesta 2014 Petrol) always have a positive long term fuel trim, which means its running lean mostly. The log data that I recorded using torque pro can be downloaded here : Torque Pro Log
LTFT always quite unstable, and swing from around 5% to 15% on lower rpm (<2000 rpm). However on higher rpm ( > 2000 rpm) it tends to stable around 5%.
First O2 sensor looks to be working normally, fluctuating from 0 - 0.9v, and second O2 sensor tends to stable around 0.65v, and occationally drop to low number for a while when I let go of the pedal before recover to normal voltage.
So I am a bit worried on the constant lean. Is it a vacuum leak?
No error code has been generated, but I couldn't trust the error code as well, as my vehicle had run without thermostat before , and coolant temp staying <= 70 C max all the time for a year, and ECU never gives any error code.