Lx470 VVTi misfires on startup, random stalling during low throttle

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Joined
Jan 25, 2021
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Location
Dallesport, WA
Hello all, I have been narrowing down an intermittent fault I keep having. Deduced the
spark plugs, coil packs are not the issue along with the battery and alternator as potential problems. It started a couple weeks ago, when we were coming back from a beach trip and the LX just died when coming down over a pass ( low elevation). Went through the troubleshooting process and after running fuel trims (see below) looking for more help from the collective group. I just cleaned the MAF, but I'm thinking after 260K miles the fuel pump might be giving up the ghost. The Torque screen shot is during minimal throttle and the attached fuel trim csv is covering bank 1&2 short term and long term fuel trims. Looking for any insight or further tshooting before I bite the bullet on a new fuel pump. Of note, my first thought is the long term looks a little off. Thanks.
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Anybody have any ideas on this issue? Do you need more context? Is there another method to testing the fuel pump?

Thanks all for any support.
 
It appears your Long Term fuel trims on Bank 2 is compensating, it should be lower (in the 0s and1s range on low rpms) and near identical to your bank 1.
Check vacuum hoses, they're on the passenger side/intake side of the engine and just make sure none is loose and/or cracked.
If those hoses are good, it can be your fuel pump. I just went through this last week,, I can relate. See this post.
 
It appears your Long Term fuel trims on Bank 2 is compensating, it should be lower (in the 0s and1s range on low rpms) and near identical to your bank 1.
Check vacuum hoses, they're on the passenger side/intake side of the engine and just make sure none is loose and/or cracked.
If those hoses are good, it can be your fuel pump. I just went through this last week,, I can relate. See this post.
Thanks OEMGUY for the response, I also noticed that as well and did check the hoses and all was good, tight and nothing was cracked. Yeah, kind of frustrating, but the fuel trims have been pretty telling as I have been driving a little and noticing some more oddities.
 
A few years ago, I had a somewhat similar issue. The 100 ran normally. I parked it. An hour later, I went to start it and it sputtered, coughed, started - ran rough - rougher at low RPM, stalled... kept doing this. I called my buddy Dugan who happens to own ACC Garage - a Land Cruiser shop. He suggested cleaning where the actuator plate seats in the throttle body. (wiping with a very clean microfiber)

I had a crappy set of tools - one of those dumb screwdriver things with socket attachments - and spent 20 minutes getting to the TB and 5 minutes cleaning it. But it worked.

Full disclosure: I called Dugan back and told him it worked. He responded, "Holy *&#%. I gave that a 5% chance of solving it. But, with your tools and knowledge (yeah), that was about all I could think of that you could do there." I now carry a much better collection of real tools... but same knowledge.
 
I replaced the fuel pump and the tensioner pulley assembly over the weekend, and that seems to have solved the problem. The fuel trims look much better now. I think the tensioner was a contributor, but I don't want to speculate until I have the time to pull it apart and inspect it further. The bearing on the pulley was replaced, but it was still squealing something fierce on the inside of the assembly itself.
 
Hey all, I could use some help. It seems the above didn't fix the problem. It was good for about 2 weeks, then it started acting up again. The misfires came back and it really acts like a fueling issue. The below are 2 different screenshots on startup. I tested the fuel pump, EFI, and air/fuel ratio relays, along with the MAF. All fuses were inspected under the hood and in the cab on both sides. All were good. I am getting random misfire codes and individual misfires on different cylinders almost every time. The vehicle will throw a check engine code and the VSC code, then it will randomly turn off, then misfire again, then come back on again. That is a new one, that is really throwing me for a loop. Could this all be coming from the ECM starting to fail? Any recommendations? I have read quite a few of others that have experienced similar issues with the VVTI and it would be nice to get feedback from those who have experienced something similar. The first screen shot is after the engine has gone through the cold start and settled into a nice idle. The second screenshot is after startup and and starts misfiring. Any help would be greatly appreciated. Thank you.
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Misfire either on a specific bank or plug is related to fuel-air combustion being out-of-spec reading by the sensors. Have you checked your spark plugs to check if the tips are clear of any carbon deposits? Here’s mine;
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If you are running the factory ignition/coil plugs from 06/07 just like me, I think it would help if you include that in your troubleshooting process.
Advancing to your troubleshooting, check your vacuum hoses and make sure there is no crack or leak, the 2UZFE VVTi from experience is a little more sensitive of these delta and it will more often than not throw a code or ripple to a misfire error similar to what you are experiencing. Fully inspect the ends of the vacuum hoses as the leak is always there, check the underside unnoticeable just by eyeballing it.
Also check your upstream (AF sensor) and downstream (O2) sensors make sure they are not contaminated with carbon deposits, if they are it’s time to replace them.
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Thanks @OEMGUY0720 Its always good to go back and start with the obvious. The plugs and coils was my initial starting point. I swapped the new coils and plugs back in and below is a pic of the old plugs. These dont seem to be to bad and are about 5 years old and what I changed when I initially bought the vehicle. I plan to go through the vacuum hoses more in depth this week. More to come.
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Do you have the AF and O2 sensor voltage readouts on your OBD app? If so, a good troubleshooting approach is verifying if both Banks are operating in the same voltage range, doesn’t have to be the exact value but delta should be within decimals.
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AF (airflow) aka upstream and O2 (Oxygen) aka downstream sensors are 2 sensors responsible for sending the ECU accurate temperatures on the exhaust system to either advance (rich) or retard (lean) the timing. Too lean will give you really bad MPGs and engine will run hotter. If any of these 4 sensors are not picking up the accurate data, it will send false information to the ECU hence the retard/advance timing.
The UZ engine family is actually simple, it’s combustion system have misfire triggers:
• MAF sensor (by the air box filter) to measure the amount of air flow measured in CFM
• spark plugs (controlled/timed arching spark from coil plugs)
• coil plugs (electrical pulse converter)
• AF sensors (upstream) to measure the exhaus temperature gases if the engine is running hot or within spec.
• O2 sensors ( downstream) to measure amount of CFM oxygen flowing in the catalytic baffle for emission purposes.
• vacuum lines/intake lines (this has to be air tight) to feed air in the intake plenum while engine is sitting idle when the throttle body is closed.

If the misfire is predominant during idle, it’s likely a vacuum line or a leak in the throttle body gasket since the intake manifold is not getting adequate air or leak in the intake tube post-MAF sensor.
If the misfire is predominant during operation from 1st to 5th gear, it’s likely the first 4 items on the list.
 

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