DanielleAlek

First post! I'mma start off positive by posting a pic of my beautiful lady! Old pic, you can tell because no snow:

SHE'S SO PRETTY!!!


Tl;dr: Slight rough idle with occasional small "hiccup" or "shudder", both banks running lean by around 12-18%, then P1349 appeared today. Car is running catless, so it has P0420 and P0430 (not my fault, it came like that, I'm getting cats soon). Dunno if these issues are all related or if they might all be independent.

I'm at my wits end with this one. Yeah, you can read the title and go "Have you searched?", and yeah, I have. I've read every forum post, watched every YouTube video, I still can't figure this out. I'm gonna be as detailed as I can be in case someone else can catch something else I might've missed.
So, I have a 2002 Lexus GS300 with around 203k miles. I got it in kinda rough shape, had a huge vacuum leak, needed a new PCV valve, and the previous owner ran it catless. I fixed the vacuum leak and got a new PCV valve, I don't have new cats yet, but I'm getting them soon.
Everything was running great after all that.
The vacuum leak was the usual suspect on these GS models; the air intake resonator box. I was cheeky and just used high-temperature electrical tape and duct tape.

The first indication of my work not being done was when the VSC and TRAC lights came on, so I took out my scantool as soon as it was safe and saw P1349.

The first P1349 code

I had no symptoms at this point, and as it was my only vehicle at the time, I did the "easy fix"; I changed the oil and reset the computer. It seemed to go away.
While taking an out-of-state trip, it came back, and this time, it was showing some major symptoms. Occasional rumbling shudders throughout the car, like it had a misfire, but only at idle, and I had no timing or misfire-related codes. Just P1349.
Unfortunately, I had to drive the car two hours back to my house in this condition, and that only made it worse.
During most of the drive it was fine, but whenever I had to idle, the problem made itself known. By the time I got home, the idle was so bad I decided I had no choice but to garage the car until I could fix it, it was barely drivable and I was concerned about doing serious damage.
When I finally fixed it, I replaced the VVT solenoid, oil control filter, and all the coils and wires, just for good measure. I didn't replace the spark plugs, since I had just done those in September, a couple thousand miles ago at the most, I think.
P1349 went away, and the car was idling MUCH better.

Here's an important note; I specifically looked to see if there was any signs of a leak in any of the cam gears. It seemed completely dry to me, and the belt itself seemed fine (a couple nicks, but I've definitely seen worse). This, paired with the fact that I'm getting no timing-related codes besides P1349, made me believe that I didn't need to change the timing belt or VVT cam gear. This isn't a piece of info that comes back later, but I'm stressing it in case I'm doing something wrong here; should I change the timing belt and VVT cam gear just to be safe, or is that just me throwing money at the problem instead of fixing it? Should it be further back on the gears? Below is a picture of the nicks in the timing belt, along with how far forward it is on the gears:

The nicks in the timing belt


After a while of driving, though, the idle became a bit rougher, and sometimes, you'd get these slight "shudder"-like feelings. It felt like it might've been a misfire, but nowhere near as severe as before.
I looked at the live data, and it was running lean on both banks, in the range of around 16%-24%, just under what it'd take to trigger the CEL.


Running lean by 19.5 and 23.4%; just below what it'd take to trigger the CEL.

Oddly enough, though, unlike a vacuum leak, it would increase with RPM, with it hovering in the low-mid 30s at around 2,500RPM.


Running 33.6% and 32% lean at ~2,500RPM

So, I replaced the air intake resonator box, no longer content with my duct-tape job, cleaned the MAF, changed the air filter, and reset the computer.
After this, the fuel trims were fixed, and then gradually climbed back up until they plateaued around the 12-18% mentioned in the title of the post. They tend to stay around 12% on bank 1, and 16% on bank 2. Was disappointed they weren't just fixed, but honestly, it's such a massive improvement that I felt like I was at least making progress in the right direction.
It also started behaving more like a vacuum leak; at higher RPMs, the trims go down to around 0, like you'd expect. High fuel trims at idle, normal while accelerating and coasting.


Fuel trims acting much more normal than before at idle, 8.6-10.2 in this image.

After this, it started running even better. The idle was still a bit rough, but it only manifested itself as a slight vibration in the steering wheel, with the occasional, very rare little "shudder" or "hiccup". These had become so subtle that if you had the windshield wipers on or music playing, you couldn't even notice it.
The stupid aftermarket exhaust manifold the previous owner put on is NOT good, and was NOT installed properly, so I had to come up behind them and fix that. I'm getting an OEM one soon, and I honestly genuinely thought that would be it; after the exhaust manifold was replaced, the trims would go down and the vibration would disappear. I really thought that.

But today, the VSC and TRAC lights came back on. I was luckily right by my house, so I immediately pulled out my scantool and yep, P1349 was back.

P1349 Episode III: Revenge of the VVT

I was so dejected and upset, I just had to make this post to see if anyone has any ideas. Can I reseat the solenoid and connection, reset the computer, and hope it doesn't come back, or am I doing damage to the engine without knowing in the time it takes for the light to come back on? Could it be a valve timing issue even though I don't have any timing-related codes? I also noticed while making this post, I had overlooked that the throttle position sensor reading is 17.3%, isn't that around 3% out of spec? Is that enough to cause an issue?
Am I at the point where I need to just start throwing parts at it? New timing belt, new VVT cam gear, maybe some new vacuum lines and gaskets to deal with it running lean? Am I an idiot for not replacing the timing belt after seeing those little nicks? What am I supposed to do at this point? I could really use some guidance, all my mechanic friends are kinda stumped, too. One suggested double-checking all the grounds, still haven't done that.
Thank you for any and all responses, especially if you took the time to read all the details!
My reader is ****ty, so instead of spamming more images, I'm just gonna type a live data snapshot here:

Engine coolant temp: 92C

Short-term fuel trim bank 1: 3.9%
Long-term fuel trim bank 1: 8.6%
Short-term fuel trim bank 2: 7.0%
Long-term fuel trim bank 2: 10.2%
RPM: 660

Spark Advance: 18 degrees
Intake-air temperature: 38C
Mass airflow sensor: 3.25g/s
Throttle position sensor: 17.3% (seems 3% out of spec, could this be a clue?)

O2 sensor bank 1 sensor 1: 3.325V
O2 sensor bank 1 sensor 2: 0.740V
O2 sensor bank 2 sensor 1: 3.255V
O2 sensor bank 2 sensor 2: 0.680V
LAMBDA11: 1.007

Once again, thank you so much for reading this far. I really appreciate it. Have a great day!

CurlyG

Have you done a smoke pressure test of your intake system? On my 2GS400, I found a leak under the intake manifold, which was caused by the plastic core of the sheetmetal top/bottom gasket, which had 2 small cracks that were letting in air.
I also found smoke falling down from the gas tank when I smoked the Evap system. Found a cracked plastic valve/hose fitting on top of the gas tank.
I was chasing CEL's for weeks, until I bought and used the smoke test kit.

DanielleAlek

I've been dealing with a lot of leaks in my SUV, so I was gonna get a smoke test kit next paycheck.
I don't really see how that could help with the VVT issue, which is the main thing garaging the Lexus rn, tbh

CurlyG

Think about how fuel trims work, and I'll try to remember myself: The front 02 sensors are reading the amount of unburnt oxygen in the exhaust, which then signals the fuel trims to lean out, or enrich the mixture, to keep the A/F ratio nominal.

If you have an intake leak, the front 02 sensors detect too much unburnt oxygen (a lean condition), and add more fuel (positive short, and long term fuel trims).

If your A/F ratio is too far out from nominal, perhaps it sends the VVT system a value that is too high or low for it to operate?

Also, if the engine has ran smooth, that indicates that your timing belt is timed correctly. Looking at the photo of the belt, I would absolutely replace it soon. Sealing the water inlet (which contains the thermostat, and sit above the timing belt) was the most difficult part of the job. The first time, it leaked, and all over my new timing belt. You have to apply RTV to one end of the joint, and then press it, then hammer it with a rubber mallet into place.

The first thing I would do is, as you said, seal up the crappy headers, or put the OEM log on: Any exhaust leaks in front of the front 02 sensors will throw off the reading, as the system is no longer closed. I believe the rear 02 sensors simply monitor the emissions reducing performance of cats.

Since you mentioned vibrations, I'd also look at the engine mounts. I check by popping the hood, starting the engine, pushing and holding the brake pedal, then flicking the throttle with my heel, ensuring that the brakes are fully engaged. Peeking through the bottom of the hood, I check if the engine rocks or rotates upward, indicating that one or both of the engine mounts are bad. I replaced my engine mounts with non-name mounts, and 10k miles later had to replaced them again, this time with Toyota mounts.

dwoods801

Sorry for the long reply, there was several questions I was trying to answer

StevensVenita

Any update?

JonGS3

Here's the FSM procedure for diagnosing that code: https://charm.li/Lexus/2000/GS%20300...0Charts/P1349/

I didn't see it mentioned which year/engine you have so I pulled the 300 but that link has FSMs for all years and models.

JonGS3

Also, it looks like all of the specs you measured are pretty much in line with where they should be except for those two O2 sensors reading high: https://charm.li/Lexus/2000/GS%20300...%20Conditions/

dwoods801

Pour a can of Seafoam into the engine oil and then let it idle for 45 minutes. Then change your oil, and reset the CEL, this should solve the VVTi problem.

DanielleAlek

I've garaged it for the winter, I've starting focusing my attention towards a couple other cars until I have the money to address the exhaust manifold (those things are expensive, yo).
I'll make sure to update you when I start working on the GS300 again.