I have an ‘99 GS400, so the 1UZ which is very similar to the 3UZ in your LS. While chasing down a vacuum leak on my engine I realized that it has only a few systems running off manifold vacuum pressure. Theses separate systems the EVAP, Power Steering Idle Control Valve, and the Brake Booster involve a few feet of vacuum hose running from the manifold after the throttle body and then to complete the circuit and not just be a vacuum leak, they run another vacuum line to the air intake somewhere between the MAF and the throttle body. So quite a bit of hose plus the component that is utilizing the vacuum pressure. So each system could be hiding a leak and difficult to find even with the smoke machine. I realized that it’s not difficult to just cap off the vacuum ports on the manifold and intake tube for each system to eliminate any hidden source of air and was able to rule out a vacuum leak without having to build a smoke machine or pay someone to use theirs. This will cause a DTC for the system that temporarily won’t be getting vacuum pressure, but that is obvious, just mentioning so you’ll know to keep track of the codes and make sure u don’t pick up any new ones.
A vacuum leak is the most common cause of a lean system code. But I don’t believe you would see limited rpm’s as a symptom of a vacuum leak. If the intake had a restriction the prevented enough fresh air from flowing could restrict RPMs but that’s unlikely. Also an exhaust restriction could limit the RPM’s like when a catalytic converter disintegrates and the catalyst collapses into itself preventing the exhaust air from escaping and restricting the engine from reaching maximum rpm’s. But this would probably show as a distinct problem with 1bank and not similar FT’s on each bank. So this still points to some type of any issue with fuel. Did you replace the fuel pressure regulator yet? Have you got the freeze frame data from the O2 sensors? The .#1 sensors on each bank could be helpful if you have them available and would like to post them when u have a chance. Also, if you want to eliminate vacuum leaks like a suggested, it’s pretty easy. Just get a few pieces of vacuum hose from a parts store. You need 2 pieces of each size that the ports will be. I would suggest ‘2 of “1/4 “5/16 and “3/8. Cut each piece into “12 lengths then fold each piece over and zip tie it close to the fold. When folded over and zip tied it’ll give it a tight seal. And then you just need to push the other end onto the port. You want to do each system separately so you can isolate where the leak is, if your able to determine there is a leak. So you’ll need to identify both ports for each system and get them both sealed off. Then fire up the engine and let it run for a bit. If it’s not a critical system, like the evap system, you could clear the codes and go for a drive. See how the FT look. The only system that was difficult to do this with was the brake booster. The vacuum port is on the back of the manifold and I believe it was larger than the others if memory is correct. There is also a system on the bottom of the manifold that controls the variable intake runner length. It might be hard to find the ports for it, if theyre on the bottom of the manifold. It was 5 years ago I did this. And I am trying to remember all the details. If you want to tackle this, I am happy to help, just send me a DM if u have any questions.

 

Thanks to everyone for all the great info and help. I appreciate it all!!! For real I learned alot from this

I ended up at a Japanese auto repair shop where they found a leak in a hose. $121 for part and labor.
lean codes are gone. Car is running beautifully. They said that code p1354 kept coming back after they cleared it. But i just drove it pretty aggressively and so far the code hasnt shown back up.

hopefully this is the last update!

 

That’s good to hear, I have been feeling guilty for insisting that the fuel pump would fix it. After looking at the freeze frame data, and the lean condition being worse at higher rpm’s, I was really expecting it to be a fuel starvation issue and the fuel pump is generally always the solution when it shows leaner conditions at lower rpm’s. But I guess not being able to reach higher RPMs may have hidden the results from rpm’s near redline. It’s not normal for a vacuum leak to effect the engines ability to reach redline. Wasn’t that symptom worse before the fuel pump? I really still think your fuel pump may have been part of the problem. I am only asking so any future members who may have similar symptoms can learn from this and hopefully not have the hassle you went through. Seems like the P0171 code can be a real battle to solve.

 

P1354 and vsc off came back just now but no lean codes.
i had replaced the solenoid fairly recently already.

the same shop quoted me $500 for part and labor which seems high for a solenoid that I can replace myself.

Will post trip data soon

 

I feel the car performs so much better after replacing the fuel pump. Even if it was not the solution, it definitely helped a lot with the performance and shifting. Very worth it. After replacing the vaccuum hose leak the car reaches all the rpms for the first time! I got it to redline for once

 

Well I am glad you got it fixed, and as I said when suggesting you just go ahead and replace the fuel pump, you are at a point where they start failing, and never last forever. So if it wasn’t the issue, it likely would need to be replaced in the future anyway. So maybe it was weak and just a coincidence that there was also a vacuum leak. Thanks for updating the thread.

 

would you still recommend replacing the regulator on the fuel pump as well? Right now all that I replaced was the pump and housing assembly.

 

i have never replaced mine, if the car feels and performs as well as it ever has, I wouldn’t worry about it. I don’t believe the regulator would be considered a wear item that you can expect to malfunction at any particular time. Certain parts of an expected life span and others are much less predictable, if it could possibly last for another 100k or more, and there isn’t any depreciation of performance as it ages, not worth replacing until there is a problem. The Average lifespan of an automotive fuel pump seems be about150k miles, across all manufacturers. The regulator’s lifespan can have much more variation.

 

P1354....VVT related. Given your solenoids has been changed recently lets park changing them again for a moment.

What grade of oil are you currently running?
And what are the air temperatures where you live at the moment?
Has the oil been changed recently? (in terms of date and distance)

If you remove the timing belt inspection covers, are there any visible oil around that area? (cam seals, and or cam variator)

 

Oil change was done 800 miles ago, cant find invoice but I’m 99% sure it was full synthetic. Previous oil change was between 3000-4000 miles prior.

I’ll take a look as soon as I get a chance. What are the specific areas that the covers are located? This is my first time looking at the belt inspection covers

 

Here are the inspection covers - you only need a 10mm spanner to remove the covers. 4 screws each side and 1 nut.

Be gentle on the wires and connectors as they ten to be a bit brittle from years of engine heat exposure.

 

Thank you. Quick update, I cleared the codes after my last post and have been driving the car a little more aggressively when accelerating. So far the car has been driving beautifully. Better than ever. P1354 has not come back...yet. I expect it to come back again lol but it's been a few drives without it so far. Once I can get my OBD scanner working again I'll post more data to compare. Will be checking those inspection covers too.

edit: also just replaced the battery after it died on me today. Car wouldn't start without hesitation and was clicking. Shop next to my house told me the starter was bad (even tho it was replaced at 101k). Japanese speciality shop I called says it's the starter lol. Took it to Autozone and they told me bad battery. Put in a new battery and all is good lol.

 

If the code has cleared and it is driving well just relax and enjoy.

Sometimes erroneous codes are set due as a second order problem. I had a p1350 (same but other side of the engine) appear once after bad fuel killed my knock sensors. Probably got set when the computer was trying hard to counter pre-ignition. Fixing the knock sensor issue and the 1350 code disappeared.

 

Car is still driving alright. I get code P1354 here and there but when I clear it I can go days (even a whole 125 miles at one point) without seeing it again. Seems very infrequent but still there... haven't had any time to dig into it lately. Usually just driving it to and from work two miles away so it's been fine. some days car runs beautifully, other days it'll downshift kinda hard randomly while going. love this car but it's alot of stress lol

 

So a P1354 if it keeps coming back is something to do with the VVT system on bank 2 not behaving as expected.
As noted you have already changed the VVT solenoids and the wiring.

Which leads to the next thing - Oil & Pressure

Again is/was there any visible oil in the areas mentioned before around the belt inspection covers?
What grade of oil are you running? 5w-30, 10w-30, 10w-40?
Is it between low and high on the dipstick?
What are you current low and high air temperature where you are driving the car?
How long in months & miles was it last changed?

One last question - did you inspect, clean or change the solenoid oil filter then the solenoids were changed?
If these little filters are gummed up, the vvt mechanism is potentially not getting enough oil flow to function properly.
Unlike the 1JZ which is easy to get to the filters, in the UZ motors you have to remove the rocket cover, the timing belt cover and take off the front cam holder to get access to the filter