tadiguy

I have 2006 RX330 that is giving me P0171 & 0174. I has 189k troublefree miles (with regular maintenance) until now.
Observations/Symptoms

1. A little vibration at idle and lack of power under load
2. P0171 & P0174 codes set after two drive cycles. Freeze Frame confirms problem happens under load
3. Live monitoring of LTFT under load is high for both bank 1 and bank 2 (25 - 40%). STFT is OK. LTFT and STFT are both OK at idle
4. I don't hear 1-2sec Fuel Pump priming with key on (I don't remember if I used to hear this on this vehicle - can someone confirm this)
5. Replaced spark plugs and cleaned throttle body 10k mile ago (and timing belt/water pump 20k mile ago)

Troubleshooting Efforts So Far:

1. Fuel pressure check OK at 44 psi at idle and under load; residual pressure sits at 30% for more than 15 minutes
2. Replaced fuel filter - not the screen but the filter canister that wraps around the pump assembly
3. Cleaned MAF sensor and inspected all vacuum hoses. Flow rate is about 5 g/s at idle
4. Vacuum leak test with smoke machine - no leak detected (not surprising since lean condition is only under load)
5. Replaced PCV valve (was due for replacement anyway)
6. Nothing seems out of the ordinary (except LTFT) when I monitor live PIDs data.
7. Fuel pump resistance test measured 0.6 Ohm which is within spec according to FSM (a new Denso pump I have also measure 0.6 Ohm so didn't replace fuel pump)
8. Removed and inspected main ECU. No obvious sign of component damage. With exception of SRS/ABS parameters I can't read any ECUs with Techstream, not even in generic Techstream OBD mode which is why I wanted to check the ECU. However, $30 OBD scanner works OK and Techstream works fine on my 45
9. Intake Air Controller actuator works OK and no sign of RPM change when I move it (was the culprit for member HtownBlue in post https://www.clublexus.com/forums/rx-...174-codes.html

Next Steps
I'll clean the injectors next after I get my hands on a FI cleaner kit. I know many other things can cause P0171 and P0174 but I have been focusing on fuel delivery system (since lean condition is only under load) and things that are common to bank 1 and bank 2. If anyone has any thoughts about what else I should check or re-check please let me know.

JoeInHNL

This article was helpful to me in diagnosing a bad wideband sensor causing P0171:
http://www.underhoodservice.com/trou...nd-o2-sensors/

The procedure for the testing wideband sensors in the section titled "BAD A/F SENSOR OR SOMETHING ELSE?" confirmed for me it was a sensor problem. Although I think it is unlikely that the wideband sensors on both sides would fail at the same time, it is a quick and easy check to confirm your sensors are responding normally.

numbafree

This might be helpful:

https://www.clublexus.com/forums/rx-...174-codes.html

tadiguy

Thanks, but that's the HtownBlue post I referred to in my bullet #9.

tadiguy

I noticed that my Throttle Position Sensor (TPS) only goes from 15% at idle to 49% at WOT. This doesn't seem right and could signal the ECM to inject less fuel to cause the lean condition. I'll do some more troubleshooting on the TPS. If anyone knows what normal range is on the RX330 please let me know.