Again, this is a 2002 Nissan direct injected engine (QR20DD). By judging spark plugs, I assume that the air / fuel mixture is not rich. May be some kind of a lean condition?
But the issue is fuel trims. When it idles around 650RPM, the STFT is bouncing from -2% to -8% and the LTFT stays at -10%. STFT is 0% to 2% and LTFT is -5% at 2500RPM.
Whaty I don't understand is why the spark plugs indicating a lean mixture and fuel trims indicating a rich mixture?
I understand that the rich mixture at idle and fuel trim close to 0% at 2500RPM is an indication of a bad MAF sensor. But it reads pretty OK (1.25V - 1.32V) at idle. May be the intake valves are clogged or any other causes?
