Disclaimer- New here so point me in the right direction but really struggling to find what I need. Fairly competent in diagnosis but also not a professional by any means.

My 2015 lexus gs350 awd started running lean with noticeable hesitation usually at lower speeds and bogging down after longer drives at highway speeds. 30 mins around 50-70 mph. First hesitation is at slow acceleration leaving my house. Second is 30 mins after exiting freeway where my car almost stalls at the same light with trims exceeding 20-30%

At idle LTFT around 7-12 and climbing until STFT goes to 0 and settles out.

MAF sensor changed but still seeing permanent circuit high codes. not sure if that's from unplugging them or not yet. Only reason I'm not sure on this is fuel pressure changes.

Upstream air ratio reading 3.3 V. Downstream seems to show rich 99.2 and 8.95V at idle. No significant changes under throttle.

HPFP pressure rail showing around 2000 but drops under throttle to around 600 and slowly climbs back up. This is leading me to fuel issue but I'm not super familiar with HPFP and LPFP and how they relate in this system. I'm led to think that lpfp could be failing/fuel filter/regulator leading to not enough fuel at HPFP under throttle.

No leaks in either set of injectors from what I can see and smell. Port injectors have been changed out as there was a previous code for those.

Exhaust and intake have been smoke tested for leaks. Nothing found. Evap system was tested and leak at gas cap was found. Waiting on gas cap now. Wondering if exhaust leak could develop when warm and be intermittent.

P0103 and Lean bank 1. Both banks are running lean however this seems to be intermittment as well.

let me know if any other info will help. I'm on month two of trying to fix this. Help!

 

LTFTs are the same for both banks?

Have you checked your fuses? What do you get for MAF sensor feedback?

 

Welcome. First of all how many miles on the GS now? Where did you get the MAF you replaced from?

On your last OBD scan what exactly do you see now coding, what codes exactly?

 

Once warm LTFT bank 2 goes leaner by about 6% usually settling around 12 and bank one settling around 6 at idle. When my car bogs down usually it's after both those numbers shoot up over 20% as I described above. Where it's gotten tricky is I've seen one go much leaner first and the other follow.

Will check fuses now. MAF reading 6 at cold idle and settle around 3 g/s. Replaced with oem denso.

 

sitting at 94k miles. MAF from autozone oem denso. Originally did buy an aftermarket and trims were worse so took that back and got the correct one thinking that could be my problem

permanent codes are P0102 and P0113 usually with a lean bank 1 or 2.

 

As I have a 2015 as well and just found my problem yesterday after seeing readings of 14-22 on bank 2 of LTFT. I've noticed in the mornings that I have been having piles of broken pecans on top of my driver side strut tower. Before I would just knock the pecans off and carry on. But this time I started really looking around as I believed this has something to do with my issue. What I found was what I believe to be a squirrel has created a vacuum leak on a vacuum line. This line is the one that goes from the back of the car and runs up through the trans tunnel and goes into the intake manifold or the valve cover, can't remember all of a sudden. It's the only vacuum line that is very obvious on the driver's side attached to the strut tower. Found multiple splits and cracks to which I temporarily put aluminum foil tape over. BOOM!! Problem gone and the car idles so much smoother now and also has a lot more power down low in which it hesitated before. Give it a look and see what you find.

 

As I have a 2015 as well and just found my problem yesterday after seeing readings of 14-22 on bank 2 of LTFT. I've noticed in the mornings that I have been having piles of broken pecans on top of my driver side strut tower. Before I would just knock the pecans off and carry on. But this time I started really looking around as I believed this has something to do with my issue. What I found was what I believe to be a squirrel has created a vacuum leak on a vacuum line. This line is the one that goes from the back of the car and runs up through the trans tunnel and goes into the intake manifold or the valve cover, can't remember all of a sudden. It's the only vacuum line that is very obvious on the driver's side attached to the strut tower. Found multiple splits and cracks to which I temporarily put aluminum foil tape over. BOOM!! Problem gone and the car idles so much smoother now and also has a lot more power down low in which it hesitated before. Give it a look and see what you find.

 

That was going to be my next post.

The Rodent issue is the #1 problem when you see this on the Lexus. It's in every Lexus Model forum. You likely need to check in your Intake housing and tube to you TB, and look to trace chewed up wiring and/or tubes some where that creating the voltage reading problem to the MAF.

 

Additionally to my last comment, the other thing I was experiencing was when I went full throttle a big plum of black smoke would plum out from the exhaust. This would only happen initially but quickly cleared up as I continued the pull. But as a by-product of all that unburnt fuel going through the cat, I would get the sulfer/rotten egg smell that would linger for a bit. Being that there was a vacuum leak, the computer tried to compensate for all that unmetered air and just dumps fuel to try and compensate. The cat can't effectively burn all the extra fuel which turns into a black smoke screen to who ever is following you 🤣. If you believe you may have a vacuum leak just listen around your engine for a hissing sound or get brake clean and spray around any vacuum lines. Listen for the engine to rev up since its sucking in addition fuel from the brake clean and make it a little easier to locate the leak.

 

Denso MAF is good, but I've bought "bad" knock-off denso spark plugs from Advance Auto. I now only buy from Toyota or Lexus.

 

that's interesting because I've had a similar finding of some sort of pinecone remains on passenger side near all the grounds and a large group of wires. Can't wait. This will be fun.

 

Have you had a chance to glance around and look at some of those vacuum lines?

 

really wish I found more. Found some chewed wires that ran into the driver side wheel well. Fixed those.

Im not sure I'm looking at the right places for all the vacuum lines. Is there a diagram for these? Checked the PVC valve, brake booster, purge valve, one off the snorkel.

 

You need to be sure to chase off whatever is chewing through the wiring. Else you'll just be chasing gremlins as it does more damage.

 

random direct injector code this morning that I've never seen. Didn't mess with any of that system. This is messed up lol.