201object8 Toyota RAV4 - P0171 Lean Bank 1 - Rough Idle and Stalling

Question

Getting a P0171 Lean code on my wife's 2018 RAV4. The Long Term Fuel Trims (LTFT) are sitting at +25% at idle but they drop down to about +5% when I'm driving at highway speeds. This usually points to a vacuum leak but I've sprayed carb cleaner everywhere and can't find a leak.

The car feels sluggish and occasionally stumbles when coming to a stop. I've cleaned the MAF sensor and it didn't change the trim values at all.

ChevyChuck · Answer

✅ Confirmed fix: Replaced the A/F (Air-Fuel) Ratio Sensor on Bank 1 Sensor 1. Even though it didn't throw a heater circuit code, the sensor was skewed and reporting more oxygen than was actually present. Swapping it with a Denso OEM sensor brought the fuel trims back to -2% within minutes of a test drive.

SuspSpecSal · Answer

Check the intake manifold gasket. On these 2.5L engines, they can leak when cold and seal up slightly when the plastic expands. Since your trims improve at RPM, it's definitely an unmetered air issue.

201object8 Toyota RAV4 - P0171 Lean Bank 1 - Rough Idle and Stalling

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