Hello guys and girls, I just joined the club, thank you for the wealth of information that you make available.
I bought a 99 rx300 (2wd) about a year and a half ago in Florida. We moved to MA on December of 07, (driving on it)

Given the cold here I started going to have the oil changed at Valvoline quick oil change places (i used to do it myself in sunny FL), the last time I went the guys there suggested I clean the fuel system, given I hadn't done it I figured it needed it anyway at well over 100k, so I went for it and about 3 weeks later the car started idling rough and stalling. I'm kind of a do it yourself guy (when things aren't too complicated) so I went to Autozone, got the codes, seemed a relateively easy fix. I replaced the sparkplugs (used the same as recommended by manual) didn't fix it, went to a backyard mechanic, didn't fix it, then I had to go to a shop.

This was the diagnosis:
codes P0300, P0301, P0303, P0305, P1300. no vacuum leaks in system, fuel pressure OK. Trace to bad ignition parts. It was recommended to customer that all coils be changed, customer decided change only for cylinders 1,3 and 5. (mind you, when I went wht the backyard mechanic he swapped the coils from back (1,3 and 5) to front (2,4 and 6) and that didn't make a difference, the same codes came up)

The rough idling and stalling went away, however as soon as I rolled out of the garage the check light came on again, went back, they hooked the car again to the computer and code P0171 came up. They cleaned the Rear O-2 sensor, reset the code, and stated that the sensor may need replacement in the future. I was stupid enough not to ask for the old coils, that was my fault, but I went there after researching lots of local shops, they actually get ranked almost every year with top honors by the locals, so that's why I went to them.

So about 3 months have passed. Last night we went for a long drive with my wife (about 1 hour each way, almost 40 miles of combined city and hway each way) and the light came on, I went to autozone today, code is P0171. Their printout said Fuel trim bank one condition, computer has recognized a rich or lean condition on one engine bank only.
Possible causes
1. if bank 1 and 2 codes set together suspect fuel pressure or MAF sensor
2. Oxygen sensor defective
3. Ignition misfire-repair
4. Fuel injector problem

the autozone guy recommened I use a fuel system cleaner and possibly look into changing the o-2 sensor

now, the car has little over 122k miles, like I said before I was stupid enough not to ask for the coils at the shop, I still suspect they didn't change them but due to the back coils being so goddamn hard to reach without proper tools I left it at that (plus the car has been running ok, even now that the P0171 code is back, it's still idling ok and no stalling or anything, I just hope they didn't take my money without doing any work at all.

My questions are: what do you guys think I should do? The code points to the same fuel bank that has the new coils, I'm fretting I have to change those again!!
Also, if I change the o-2 sensor, what should I buy? I've seen OEM as cheap as $25 and Denso as expensive as $230. From reading the forums I'm still not clear on which to use, and if I have to spend the money I will, but only if I HAVE to, I mean, that's a 1000% price difference! (granted, you get what you pay for, but come on, from $25 to $230? what's with the huge difference?)

Finally, I've read on the forums and I found a thread
https://www.clublexus.com/forums/rx3...at-issues.html
that almost mirrors to the dot what is happening to me, first the (apparent) failure of coils 1.3 and 5, the replacement, and now the P0171 code... what do you recommend?

Thanks a lot!

 

Welcome to the Club.

This is the checklist for a P0171 code followed by my comments,

-air intake hoses (check the ones by the airbox and the IACV valve)
-fuel line pressure/injector blockage (run some fuel injector cleaner through the system, Redline fuel system cleaner (Pep Boys has it) is the best stuff in my opinion in an all-around cleaner
-A/F sensors (doubtful), but sometimes as a result of a crack somewhere on the exhaust itself, either right off the manifold or underneath the engine), this doesn't necessarily mean something is bad with the sensor, just that it detected something out of whack.
-MAF sensor (needs to be cleaned)
-engine coolant temperature sensor (rare), because other codes P0115, P0116 would be involved
-exhaust system- as mentioned above by a/f sensors

I have a question, have you tried disconnecting both battery cables for a few minutes, then reconnecting them and then code still comes back?

On the A/F sensors and even ignition coils, I'd highly (and I do mean highly) suggest you stick to Denso. We've had enough members use something else and eventually wind up with some issue. www.rockauto.com usually has some good prices for parts and I have used them over the years.

If there was an issue with the A/F sensors or even a coil, something other than P0171 would show up. P0171 can mean (as I suggested above) some issue detected by the A/F sensors themselves (bad gas, exhaust leak letting in air, etc.).

BTW, where in Florida did you move from?

 

Hi Lexmex, thanks a lot for your detailed reply. I read a lot of your posts before writing.
to answer your questions, I haven't disconnected the battery yet, I'll try that. I drove the car to work today and to do a couple of errands, the cel is stil lthere, but the car is running as usual, no hesitation, no rough idling or anything.
As far as the pieces go I will take your advice and stick with Denso, I was told the same thing by the mechanic who fixed it at the shop and other people I've talked to, seems this car is particularly picky when it comes to its parts! (like you mentioned too) as a matter of fact the shop bought the coils straight from a Lexus dealer in the area.

Well, I have one final question for you. I'll be going on vacation this weekend, (not driving) is it safe to drive the car these last few days (work, usual errands) and wait until I get back to change the sensors? I think it's the sensors, 3 months ago there was no leak and the same code poped up so I guess it's time to replace those suckers, but I just want to make sure it's safe for the car and us to wait, I'm leaving on Friday, the car will stay in the garage all that time, I don't think I'd get the pieces before I leave anyway.
Thanks for your advice and patience explaining things. BTW, I lived in Fort Lauderdale... and I'm missing it a lot!! LOL

Take care

 

BTW, when I said change sensors I meant the sensors in the engine bay, not the MAF on top of the airbox. I'll clean that one!!

 

Yeah, it's okay to run. I used to drive up to my 1/4 mile track for an entire weekend on a P0171 (actually the vehicle runs better at high altitude with the P0171 on).

 

just to keep you updated guys, I've not done anything... (not even clean the MAF, lazy me) but I decided go with a fuel cleaner and run that bastard up to a good speed on a nice highway drive... lo and behold, the CEL went of, the engine is working great. Isn't that something? This weekend I'm hoping to dedicate some time to this car.. but damn, it had me worried for a while there!

 

what fuel cleaner did you use?

 

i didnt know you could clean an a/f-02 sensor??

 

For starters never heard of cleaning an o2 sensor with fuel enjection cleaner.

Also my 99 Rx also had CE code pop up when the second o2 sensor under car was causing the front o2 sensor ( in the front exhaust manifold) to run extremely hot and crack my manifold...

Had the 2nd o2 sensor (under car) replaced and CE code reset and problem has been gone for over 1 year... Strange that you say multiple coils are failing... My understanding is coils on a TOY/LEX should last well past 200,000 km.

Save your pennies as o2 sensors on a lexus are "rediculously expensive" (to put it in the words of a Lexus Technician at Ken Shaw Lexus in Toronto).

Moral of the story have the MAF sensor Cleaned and the resistance on the o2 sensors checked before the trial and error replacement on parts which can be extremely costly.

 

Hi, I used a shell fuel system cleaner. I can also tell you that the damn cel is on again... I'm on my way to Autozone again to get that code out, I'm sure it'll be the same... I agree with Fern that trial and error replacement of parts is not the route to go, but this is a new problem, the initial issue was the 3 coils on one bank failing all together, which WAS resolved when they changed those coils. This new code popped up right after the coils were changed, they cleaned the back sensor (which Fern recommends too) and it went away, then it came back after 3 months or so. I have to clean the MAF sensor (on top of the airbox, completely separated from the two O2 sensors this car has) and then clean the rear O2 sensor, which did the trick before. I also agree that O2 sensors are not to be cleaned with injector cleaners, in fact there are other threads dedicated to that issue. And finally, Fern is also riht in that O2 sensors are ridiculously expensive (like anything else for this car, really) Eventually that rear O2 sensor has to be replaced, so yes, I'm saving my pennies

 

I think you should change the MAF sensor if not worked after cleaning.
Here is the link: https://www.clublexus.com/forums/rx-...de-0171-a.html

 

Two things could cause your condition. 1. your O2 sensor B1S2 or your VVT oilcontrol valve. one of those would solve your problem. If you cannot read your O2 sensor values, the cheaper part is the vvt oil controller. easy to replace but take you time in doing so. soak it with rust penetrant it could break eaisly. turn it back and forh as u pull out wards.

 

i'm still dealing with similar CEL issues and got tired of stopping at autozone so last week I ordered a bluetooth OBDII scanner for $12 on fleabay and bought the $5 app for android.

Very cool device and you can't beat the price, real time stats/gauges, detailed code reading, and the ability to clear them on my own right in the driveway. Honestly up until Monday of last week I didn't even know these nifty little things existed and I don't think my mechanic does either. So easy.

I also ordered a used handheld ($32) just so I can have another gadget in my tool box but with this new bluetooth gizmo I doubt I'll be using it anytime soon.

 

This thread is nearly 8 years old so doubt the OP still has issues or the vehicle...

Been using that Bluetooth scanner for quite some time to clear codes and agree it is a great little gadget, just make sure you get it from a good source as some of them although they look the same, will not work with different vehicle models...