Drcoffee

Im just curious if a collapsed PCV hose or capping off the PCV valve would cause a P0171 code?

or would. Burned exhaust valve on bank 1 cause a p0171 code.

Im at a loss. My rx300 has been to the dealer and they fixed the vacuum hoses and found a vac leak on the emissions system. They drove around for a long time and declared it fixed. After 200 miles the engine light came on and has a stumble. Codes p0171 and p1133 now. She says it runs better at 75mph than 60mph. Gas consumption is high. I have read all the threads on p0171 and in all these years, nobody seems to have found or at least posted the fix for it.

so it all started after she added some cheap gas. First thing I thought of is fuel injectors. Bank 1 is not easy to replace. Can crud in the fuel injectors be the problem? It blows that Toyota neglected to use a fuel filter. That simple screen in the tank is no substitute for an actual filter.. so the rx300 is in Oklahoma now and I cant fix it myself. I noticed that the fuel rail feeds the right bank first and then the left bank injectors. Would crud in the fuel block injectors 1,3,5 .

I have replaced the O2 sensors with new denso
cleaned and swapped out the MAF
fixed vacuum leaks
used sea foam in the gas

What have those affected found as their cause?

maxSteel

In my case it was a bad MAF. This video was really helpful
https://www.clublexus.com/forums/rx-...uel-trims.html

P1133 diagnostic says:

After engine is warmed up, and during vehicle driving at engine
speed 1,400 rpm or more and vehicle speed 60 km/h (38 mph)
or more, if the response characteristic of A/F sensor becomes
deteriorated (2 trip detection logic)

Open or short in A/F sensor circuit

A/F sensor

Air induction system

Fuel pressure

Injector

Engine ECU

Lexmus

My two experiences with P0171 code were both due to vacuum/air leaks:

I installed a oil catch can on the RX300, and while checking it one day I forgot to screw back in the oil level dipstick. The hole in the can caused it to throw a P0171 code.
Accord threw the code due to a crack in the hose running from the air filter to the throttle body.

If you capped the PCV and the port to the intake plenum was open, that would cause a P0171. If the PCV to intake hose was collapsed and effectively clogged the PCV valve you would get pressure build up at the valve cover, but I don't see why P0171 would be triggered.

Drcoffee

Im starting to think that this was of my creation. I installed an aftermarket exhaust flex pipe just before this started. In hindsight the pipe was about 1/2" too long and was not a perfect fit. I'm thinking I caused an exhaust leak between the head and O2 sensor. Its the only thing that makes sense after all this. Either I broke a weld or lifted the bottom of the manifold away from the head. I hope its just that simple. I will have a muffler shop refit the pipe and make adjustments if needed.

Lexmex

The PCV valve (plastic one) on my 99 RX300 has been hollowed out and breathes freely. I capped off the hole on the intake tube. Have had it like this for years and no issue. No hose.