goldfish

I am posting my experience in fixing the CEL P0171 for the benefit of our fellow enthusiast resolving this CEL. Special thanks to Lexmex and Salimshah for their patience in guiding me.

This CEL P0171 showed up last year a month after I had the smog check and registered the car, I had put it off till it was time for a smog check. I had several mechanics diagnosed as faulty sensors needing replacement.

Searching thru the forum for a fix, Lexmex advised that P0171 alone does not mean a faulty sensor, I did not replace the sensor and did clean the MAF sensor a few times, reset CEL and still went back on again. The MAF part numberfor the RX 300 is the same as the 02 Camry LE, swaped, reset and still the CEL came back on. So this illiminated a faulty MAF sensor. I followed the DIY IACV clean up steps and put it back together. I also noticed the battery poles were dirty so removed, cleaned & reassemble. I did this work early in the morning inside my garage. Started the engine, since I removed the battery poles everything inside reset and turned the radio off. With the radio off, I could hear a hissing sound inside the car, located the source to the brake pedal and it felt lighter, goes all the way to the floor. I stopped the engine, disassembled and redid IACV process, thinking I had missed to connect a hose. Did not see anything, sent photos to Salimsah and Lexmex and they did not see anything either. Put everything back together and still has the hissing sound. Since I did not want to take any chances on the brake failing while driving I called another friend mechanic and he told me that the brake booster has gone bad and the O2 sensors are bad which causes the CEL P0171. But the car was drivable.
Took the car to the shop, had the brake booster replaced and the CEL P0171 has not turned back on, pass smog check and got the car registered.
I did not have to replace any of the O2 sensors. It would have cost me to replace a part that is not broken, thanks Lexmex for your advise.

I hope this would help somebody else locate their CEL P0171 problem, its a leak somewhere. This case it was in the brake booster, most likely the brake assist hose. It fixed the problem on my RX and I wish you luck on yours.

JOHNBRAY11

Mine was the MAF Sensor.

Aprazur

Mine was a loose PCV valve.

Jerry

P.S. Put some Dry Ice in your air filter box. It can knock two tenths off your et at the track or stop light. Well...it did back in 58 on a F.I. corvette.