p0171 won't go away
 

Hi, I've had a 1999 rx300 Lexus for about 4 years now and I got it at around 240k miles, and it is now at about 277k miles. For the past 8-9 months, I have had a p0171 code (Bank 1 too lean) and no matter what I do to the engine, it won't go away.

So far I have replaced/swapped/confirmed that the following parts are indeed functioning as normal.
MAF Sensor: (I swapped this with my dad's Toyota highlander since the part is identical and neither car had a drop or increase in performance so this is working, I cleaned mine anyway with MAF cleaner)
Fuel Injectors: (Replaced some and swapped others with each other and the codes of misfiring cylinders didn't change places after cleared)
Spark Plugs: (Same as fuel injectors)
Coil Packs: (Same as fuel injectors)
Oxygen Sensor Bank 1 Sensor 1: (Replaced, I got the live data chart obd2 scanner after I replaced this)
Oxygen Sensor Bank 1 Sensor 2: (Replaced and the live data chart looked different from old so I assume is working)
Air Filter: (Replaced)
Transmission Fluid Change: (The acceleration was very bad a few weeks ago, more than normal, so we did a transmission fluid change and some of the fluid was burnt, but it is running better after that)
I replaced multiple gaskets on the Air Plenum and Throttle body
I also did a smoke test on the car to try and find a vacuum leak and didn't find anything. I also followed the vacuum hose diagram and put everything back where it should be so none of the hoses are in the wrong spot.
I have the live data charts but unfortunately, BlueDriver only shares the charts in excel format so the easiest version I have to read is screenshots.

https://cimg7.ibsrv.net/gimg/www.clu...c7f35b4434.png
This is before Oxygen Sensor Bank 1 Sensor 2 was replaced and after Bank 1 Sensor 1 was.
https://cimg1.ibsrv.net/gimg/www.clu...7408155cbe.png
This is after Bank 1 Sensor 2 was replaced with a $20 oxygen sensor
(This is my first time posting and I dont know if those screenshots will be super big or not, sorry if yes)

I also did a fuel pressure test with a rented kit, but the adapter in said kit was broken and leaking everywhere so I was only able to test the initial pressure after turning on the engine, and that was good. I don't know about if pressure lost overtime or anything else though.

Right now I have a PCV valve and grommet coming in the mail tomorrow and I'm going to check that and see if that does anything.

https://cimg8.ibsrv.net/gimg/www.clu...b265ef4d72.png
This is a list of all of the codes that come up while driving. I think p0115 is a separate issue but it might be connected. When I clear the codes, then start the car, they instantly come back.
Also, The car is misfiring in idle and has a slow and sometimes hesitating acceleration, there is no black smoke coming out of the exhaust and besides misfiring in idle and acceleration, I don't feel any problems.
I have attached the live data charts from Blue Driver obd2 scanner and I do know about the internal temperature drop that randomly happened. I believe that caused p0115 (at around 200 seconds on the excel sheet, the temperature drops from 128 degrees to -40 degrees and back up to 130)

Does anyone have an idea of what I can do to fix my car?

Welcome to Club Lexus

I don't know if cheap sensors was a good idea. See if this video gives you any insight:
https://www.clublexus.com/forums/rx-...l#post11135160

Thank you for the video, that was informative, I did replace the PCV Valve that I talked about on my post and that seemed to contribute a lot to fixing the problem, The grommet was very stiff and once I replaced it about 80% of the problem went away. But I still have a bank 1 too lean code. This time however, it came on whenever I accelerated and then turned off while cruising. I did some research and I believe something called a Fuel Injector Pressure Damper might be a cause of the issue. I am going to swap it out with a new one tomorrow and see if that fixes it, if not I will return it and go from there.

I have attached a pdf file that explains the exact problem I am having with my car, so that's why I think its the problem. (I don't know if I can attach a file in a edit sorry)

If that doesn't help then warm up the engine, clear the codes, and capture the below live data at idle and then at higher RPM's.
Hold an RPM for 10 seconds to see how the numbers adjust. Note which codes are reported first.

• RPM
• Bank 1 LTFT
• Bank 1 STFT
• Bank 2 LTFT
• Bank 2 STFT
• Mass Air Flow
• Engine temperature

Also note you have a P0115 (Open or short in water temp. sensor circuit) and the trouble areas listed for P0171 are

• Gas leakage on exhaust system
• Air intake (hose loose)
• Fuel line pressure
• Injector blockage
• Mass air flow meter
• Engine coolant temp. sensor
• A/F sensors (bank 1, 2 sensor 1)

So I put the things you asked for in there except for the coolant temperature because it wouldn't have been visible, but:
https://cimg5.ibsrv.net/gimg/www.clu...d5dcffe242.png
this part I circled was when I was in cruise control on the highway going about 65 mph. the flat part next to it was being idle in a drivethrough
https://cimg4.ibsrv.net/gimg/www.clu...1eb78c1dbe.png
same picture without the markings
I haven't put in the fuel damper yet because of space reasons, I need to at least take off the throttle body and at most the entire fuel rail. So these graphs are with the old fuel pressure damper still in.
But judging by how the graphs of LTFT max out at 52.3% the entire time it was at high speeds on the highway, it has to be something with the fuel right?

Here are 2 other screenshots I took before and after that first one.
https://cimg9.ibsrv.net/gimg/www.clu...fa54856c66.png
https://cimg0.ibsrv.net/gimg/www.clu...5d46e22fd6.png
^

I didn't get a chance to install that Fuel Pressure Damper since it would require at least the throttle body to be removed to get leverage on that bolt, but here are the graphs you asked for.
(also I just realized you asked for this when the car is in idle and warm, I will get a new set of graphs tomorrow, my bad)
https://cimg8.ibsrv.net/gimg/www.clu...d1a0945b28.png
that big flat part in the middle is cruise control at 65 mph on the highway for about 2 minutes. All of the flat parts at the beginning are idle

I bet your fuel pump needs tobe replaced, looks like your fuel pressure is not keeping up, which is why your fuel trims are so far off.

according to some videos online and looking at what you said, I bet that might be the case.
https://cimg2.ibsrv.net/gimg/www.clu...e1bfbde407.png
this is the screenshot that the maxSteel requested, 10 seconds of normal idle, 10 seconds of ~2000-2500 rpms, then back to normal idle

Can we see one screenshot of fuel trims just at idle so we can see the actual idle numbers? Idle only
>> Engine fully warmed up at idle.

Then another separate screen shot of only cruising at 45 mph with cruise control on? cruising only

With in Blue Driver app, change MAF display setting from lb/minute TO grams per second

okay, so update: I put in a brand new DENSO fuel pump and filter which cost me about $90. the fuel pump did not fix the car, BUT, something changed.
(Here are the links to the fuel pump and filter that I bought)
https://cimg4.ibsrv.net/gimg/www.clu...07905076d5.png
this is a chart of about a 8 minute drive immediately after replacing the fuel pump and filter.
https://cimg2.ibsrv.net/gimg/www.clu...14ecb8c4dd.jpg
Here are 2 photos of my old fuel pump and filter.
https://cimg4.ibsrv.net/gimg/www.clu...2e53a528a2.jpg
When the car was accelerating for the first 3 ish minutes, the LTFT would max out at 30.5% until I stopped accelerating.
Also I want to point out the MAF sensor would jump up to like 20-30 g/s and sometimes 40 while accelerating and I have no idea if that's normal or not.
But after the 8 minute drive, the check engine light would only
1. Flash while the car was accelerating
2. Turn back off after about 10 seconds of flashing and the car was cruising and decelerating.
I have not installed the fuel pressure damper on the fuel rail yet. I will do that later tonight once the car cools back down.
Thank you for all the advice so far everyone.
(Edit: forgot to mention the car is also having trouble starting up initially. I crank for about 2 seconds, then the car starts very weakly and after about 3 seconds after that, the engine feels like it gets to full power and the constant misfires start in the engine while it is in idle and parked.
Also when I replaced the PCV Valve and Grommet, the p0115 issue seems to have disappeared completely. Has not returned yet and I have put about 100 miles on the car sense then.)

Another update, that fuel pressure damper will not come off without either breaking the fuel rail or breaking something else in it's stead. If I do want to replace that one part, I will need a entire new fuel rail unfortunately. Whenever I try to break it loose with the fuel rail still on the car, the fuel rail moves with the breaker bar and not the bolt, with the fuel rail off the car, it still wont budge without heavily warping the rail.

Unless someone recommends a different part change, I will be looking into new fuel rails.

I was right unfortunately that it was this part. As far as every picture of this part online looks, it has an adjustable screw in the middle. Mine does not. (Also I lied about taking off the fuel rain in the quoted post, We had difficulties with chipped O-rings when we removed the fuel rail almost every time so we didn't try that this time.)
https://cimg1.ibsrv.net/gimg/www.clu...5c7a64783b.jpg
This is what my fuel pressure damper looks like with a boroscope camera up close.
https://cimg2.ibsrv.net/gimg/www.clu...2a17d2e868.jpg
This is where it is located on the fuel rail
https://cimg7.ibsrv.net/gimg/www.clu...9ec592c618.png
This is what it looks like online
(if your wondering what the red stuff on the bolts is, we use grease in sockets to make sure we don't drop the bolts into the engine)

Hi friend, this is hard to see what exactly the fuel trims are at idle because it's in live data mode.

​​​Need to know the fuel trims at idle.

As maxsteel requested, can we see the fuel trims numbers at idle, plus car warmed up. Need to see where those numbers settle at.

I'm sorry I can't make heads or rails of this because it's in live graphing mode.

WHAT are the fuel trims at idle, please, engine warmed up and let the fuel trims settle and post it up.

Yes please, g/cms/s.

Should be 3.0g at idle, engine warmed up