My Toyota Vitz (Yaris) 2007 randomly gives PO171 (System Too Lean) when at idle. My mechanic has done following fixes so far, but problem still persists.
- Replaced oxygen sensors.
- Replaced fuel filter.
- Cleaned injectors, spark plugs.
Also, mechanic checked for a vacuum leak by spraying propane, but he couldn't find a vacuum leak. But, he didn't do a smoke test.
Following are some scanner readings at the last trouble code:
- Short Term Fuel Trim: -0.01%
- Long Term Fuel Trim: 31.24%
- MAP: 60 kPa
- RPM: 823
- Vehicle speed: 0
It is seen that LTFT is pretty high but STFT is OK.
I checked live data and the STFT and STFT are at similar ranges at idle. When I increase the RPM, both LTFT and STFT comes to around 10%.
When I searched for the problem, I could find that if LTFT is high at idle and low at high RPM, it is probably a vacuum leak. But, my situation is different.
Also, the air pressure also varies arround 40 and 60 kPa. Could this be due to a problem with the MAF?
What else could be the cause to this issue?