I have a 2000 RX300 with about 163k miles. Did an out-of-car IACV cleaning about 2 weeks ago resulting in much improved idle characteristics. Then needed to tackle the Bank 2 Sensor 1 A/F sensor (close to radiator). Very difficult to get out and did not realize some threads were stripped until I could not seat the new sensor enough to compress the gasket/washer. Ended up stripping the new sensor threads removing it.I had a muffler shop weld a new threaded bung to the manifold and installed a new Denso 234-9009 sensor easily. Cleared all the codes. Now after driving a bit, CEL comes back on. OBD II reads p0171 (Fuel system too lean BANK 1), which is the side I did not work on. Read through more forum posts and suspected the MAF sensor, which had been replaced at about 60k miles.Took it out and cleaned with spray electronic cleaner, let it dry thoroughly and reinstalled. Cleared codes and CEL returns at idle. Code p0171.OBD reader shows LTFT as high as 39%, but on bank 2, not bank 1 as I would expect from a p0171. Maybe I am not reading this right, but it does not make any sense at this point to me.
I have also done a search under the hood for intake airleaks, since I did do the IACV cleaning a couple weeks back, and I also replaced the air filter. No leaks were found or heard.
I have not added any fuel injector cleaner to my gas yet (usually use 87 octane), but that is my next step unless there are other areas I need to consider. Any suggestions would be appreciated.

 

hey did the muffler shop weld the new bung ontop of the old threaded hole or did they cut it out and weld it in. Cause if its to high and out of the air stream it will make the sensor sense different air ratios and will make the MAF adjust causing the bank 1 to trigger a code but if its in the same place as your old threads were i would suspect the mAF is going out

 

Thanks for that. I will return to the shop and discuss the welded repair in more detail as pertaining to the position in the exhaust stream.
I have removed and recleaned the MAF sensor and added Royal Purple Max-Clean to the tank in case the injectors are less than they could be. If you get what you pay for, then this stuff must be the best (priciest). Have driven around town some, had the CEL return and then go off on its own, but OBDII shows pending code p0171, but has not set it yet again. There was also a transient p1150 that I cleared and has not returned. The voltage outputs of both bank A/F sensors are about equal and fluctuate nominally. The LTFT bank 2, still is showing levels up to mid 40% at times. This is driving me nuts, especially after spending hours reading many posts about this code and seeing that even replacement of the MAF sensor often does not prevent the code from reoccurring.Any other suggestions or directions to investigate would be appreciated. It's starting to look like an expensive dealer visit may be in my future.

 

I replaced the MAF sensor with a new one, Denso 197-6020 ($100.00 overnight from Amazon). Un-hooked the negative battery terminal for a couple of hours. Started right up and then OBDII reads just the same as before with Long Term Fuel Trim at 30 to 50 % and pending codes p1150 and p0171. Frustration would be an understatement!!!
Anyone else have similar troubles? Any other suggestions?

 

Returned to the muffler shop and discussed the length of the sensor remaining in the exhaust stream.
The new bung is only about a 1/4 to 3/8 inch thick and he did not think that would keep the A/F sensor from reading correctly. He recommended that I have a real OBDII scan run on a shop instrument and that the guy down the alley was pretty good at diagnosing these problems. Took my RX300 down there the next day and had it hooked up. After checking to make sure the timing belt had not slipped, he noted some fluctuations in the long term trend of the new sensor output. He then sprayed some carb cleaner at the base of the new sensor bung and the idle went considerably lower each time he sprayed. He suspected a pinhole leak in the weld. He spoke with the muffler guy, and I drove it into the shop so he could re-weld the suspect area. So far no new codes are set or pending. My OBDII now shows the LTFT still reading at times as high as 10 to 20 % in real time, but all the codes remain cleared and the car runs fine (always did). I may have to wait for the weather to warm back up for a final determination, since the unusual warm weather the past few weeks seemed to aggravate the LTFT %. It was at idle, stopped at a red light when the CEL would often return, and the LTFT display was reading at it highest.
If this holds, then I can get it smogged tomorrow since everything is set to go at this point. Will post back if something changes, but if this is as good as it gets, I can easily live with it as long as NO MORE CEL!!

 

check for leaks near rear 02 sensor