Shane2

I have a 99 rx300 awd. having problems.
I have changed both af sensors as well as the O2 sensor, have changed bank one and 2 catalyst converters as well as the downstream converter, have changed injectors, spark plugs thermostat, and upper intake gasket, maf sensor temperature sensor, and have examined the vacuum lines which seem fine. Am still getting po171 bank one lean as well as random misfire p1150, individual misfire codes for cylinders 2,4,6. some history; when I bought the car which has about 125 k on it last winter it was running very rich, terrible gas mileage but ran smoothe enough for my wife to use it so seeing that we live in a cold winter climate drove it she did. well this led to the main converter eventually clogging up, and I also found that the O2 sensor was dead. all of the changes I have done had little effect with the exception of the thermostat, as during cold weather she didn't seem nit was getting warm enough to leave open loop fuel, once I changed it this really brought all the other stuff to the forefront and quite frankly will not run well enough to go around the block anymore.. after clearing codes and memory she starts at 0 on both short fuel trims, once reaching temp it switches to closed loop and then bank one goes quickly to 19.5 while bank 2 goes to about the same but in the negative direction. So one bank is trying its damnest to lean out while the other is trying to enrich, and she runs like hell. I am pretty close to wits end can anybody help me? thanks Shane

fastnoypi

welcome, what brand af/o2 sensors did you use? sometimes these cars read things funny when they use anything other than Denso or Toyota OEM. Your multiple misfires along the same bank suggest a bad vvt solenoid.

Shane2

I used a bosch o2 sensor for the main catalytic converter. I assume the prior owner used denso for the af sensors, but cant verify that. I will change the vvt's out, any thoughts on the rich/lean scenario? Should I change to a denso o2 sensor in your opinion?

during operation all three sensors are reading .655 to .680, and appear to be updating well.

I appreciate your willingness to share thoughts and expertise with me, gonna get this sucker yet!

maxSteel

For the 2/4/6 misfires, have you tried replacing one of those coils?

Shane2

have not replaced any coils but the misfire never occurs until the vehicle goes into closed loop. also did not occur at all until I put in the new thermostat and the weather became warmer.

fastnoypi

There are some people that have tried Bosch and reported no issues but they are far and few between. The ones that do report problems with Bosch o2 sensors usually get the solved by using Denso or OEM Toyota, change it out. Leave the German parts for German makes.

Shane2

okay I will, thanks for the recommendation fastnoypi. typically speaking do you know a range these sensors should be reporting? does the mid .\range seem typical?

Shane2

that should have said mid .600 range seem typical?

fastnoypi

sorry, i don't know the typical ranges that are monitored. I've noticed this pattern of complaint using Bosch on several models of Toyota/Lexus and Subaru on multiple forums. Almost always the problems are resolved by using Denso sensors since they are the OEM supplier for both car companies. Car ecu's may just be that sensitive since they are calibrated with specific selected supplier parts. If you change back to Denso, at least you are being consistent in which Lexus had intended.

Shane2

thanks again for your advice and for paying attention to historical issues such as the denso one.
I will update with good news I hope once I have swapped out that o2 sensor and the vvt solenoid.