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Preface:
Yamae and I had a realization in another thread about a potentially very common issue that could affect many Lexus V8 owners. After he informed me this was an issue and not expected behavior and I fixed it, he suggested I should make it's own dedicated source of information to point people to. He had written a piece of information in Japanese - of which is presented here, translated by Google and edited by me. I then wrote the preface and explained the common symptoms, but much of the original diagnosis work was originally done by Yamae.
Application:
Those who own a car that have a 1998+ 1UZ-FE VVT-i engine such as LS400, SC400 and GS400. 3UZ-FE engines also have this problem but the range of the compensation is wider than the 1UZ-FE and the problem is not as serious as 1UZ-FE. But when the clogging is more than the ECU can compensate for, problems begin to occur.
The symptoms:
In situations where you're slowing down and the car downshifts into first gear, but without coming to a full stop (aprox 3-5mph), the moment you get back onto the throttle the engine surges and the car will jerk forward unless you are extremely careful on the throttle. I've always told friends "you have to get used to it" as anyone who drove my car would always make the car do this. This is due to the car downshifting into 1st gear and the engine "surging" to match. It feels unrefined. The car does not like low RPM, low throttle first gear. I will constantly fight the car to maintain a smooth and consistent experience.
The cause:
The issue revolves around the engine idle control air supply coming from the throttle body. This often gets clogged up with carbon. This, combined with a dirty throttle body means you need to perform service to bring the intake side of the engine to a much more natural operating situation and completely transform how smooth the engine itself delivers power to the drivetrain. The more situations I drive the car in after performing this maintenance, the more surprised by how much of a difference it makes.
Here I break down into further detail the behavior of the car:
Harsher than normal shifts. Normal acceleration shifts should be imperceptible. The allowable tolerance here is near zero. When these passages become clogged, the ECU can no longer adjust it's parameters and shifts become less buttery smooth. There are many other reasons for harsh shifts, but I noticed an improvement in shift quality after performing this service.
Difficulty controlling the vehicle speed on the highway. Specifically, you have limited throttle control on very light applications. I found it was common that I would let off the throttle because I wanted to create more of a gap between the person infront of me, but the car did not lower it's power output. I would be forced to come completely off the power and thus would slow down rapidly due to engine braking and aerodynamic resistance. I was unable to modulate the throttle below 10%. I would request 10%, 8%, 6%, 4%, 2% in a smooth curve with my foot. What I actually received from the car was 10%... 9%...0%.
Non-linear throttle response when locked in a single gear under very light throttle control. For those of you who live in mountain regions, it is best practice to preserve the life of your transmission and brakes to lock the transmission in a certain gear and use it to help engine brake going down a mountain, and to maintain a gear going up it so the transmission isn't always gear hunting. This presents a throttle control problem. I will lock my car in 3rd gear, and as I control my speed with my right foot in the 2000 - 3000RPM range, whenever I come off throttle and begin engine braking, that transition would not be smooth. Just like the previous example on the highway. And coming back onto the throttle the engine will "surge" very slightly. It was very evident the engine was having difficulty transitioning between a closed throttle and an open throttle.
When slowing down to a turn, or a stop light, it is common in normal driving to approach ~5mph, but then need to accelerate again. This is a low enough speed the car will want to be in 1st gear, rather than second. The moment you press your foot back on the accelerator, the engine will go from an idle configuration to one where it downshifts into first gear and applies power. Because of the carbon buildup, this can be extremely jerky and harsh. You will easily upset the car. One must very slowly apply throttle over several seconds to achieve a smooth transition to power. You may adjust to this behavior over the years. Observe friends who drive your car. They will easily and accidentally apply too much throttle in this situation and upset the car.
Unstable idle. I personally experienced surging idle for the first 10-15 seconds after cold-starting the car in temperatures below freezing. After that the car idled perfectly. And in warmer ambient temps the car idles perfectly. However - it is possible to have unstable idle at any temp with this issue.
Performing the service:
I rely heavily on the Japanese --> English translation in the following guide. Any mistakes are my own, the original words are written by Yamae.
Since there is no port dedicated to idle, idle control is performed only with the throttle valve. This area around this valve and the air assist system become contaminated with carbon in as little as 20,000 miles. The air assist system under the lid fixed with two + screws, which is shown near the center of this photo.
When the lid is removed, you can see the two thick holes indicated by the red arrows and the nine small holes between them. The nine holes are for taking in the measured air from the lower throttle body. The air taken in goes to the two larger holes, which can be clogged in the Celsior\LS400, especially if you frequently drive at lower speeds around town. The larger hole on the left is connected to the four injectors in the right bank, and is designed to send air to the injector's air assist port. The large hole on the right is for the left bank.
This photo shows the engine conditioner being injected by inserting the nozzle as far as possible into the hole on the left side. After warming up the engine, it is sprayed while idling. However, because this causes the engine to bog, it is necessary to spray with the right hand and control the throttle with the left hand so the engine does not stall. Or have someone in the car manually control the throttle. Sometimes it is effective to blow this hole with an air compressor in addition to using the conditioner. The point is to forcibly push the carbon that is clogged in the system into the cylinder. If the engine is very dirty, one can may not be enough.
Do the same on the right side as well. The solvent I use is Drive Joy's engine conditioner for EFI cars, but be aware that using a strange one can deteriorate the plastic of the injector.
In 3 and 4 above, the hole where the nozzle is inserted is the part indicated by the red arrow in this figure. Now you can see how this hole connects to each injector.
I first cleaned this line almost 10 years ago, but since then, I've been asked to help him or the car shop I'm in and out of. I was allowed to do this work several times. For one, it was useless to use 2 cans + a compressor, so it was necessary to remove the injector and clean it with ultrasonic waves. This owner was a person who used regular gasoline.
Editors note: You also may want to perform a traditional cleaning of the throttle body valve itself, as this will also contribute to the accuracy of the engine and your fine-control over it's power output.
When you perform this service, the difference is incredible. Every single situation and thing I describe vanishes completely and the car drives remarkably better. The throttle feels much smoother and buttery smooth. The difference is more stark the slower you drive the car. You have so much better control over the throttle in parking lots. The engine feels... "tighter", smoother. The transmission shifts are smoother. It's incredible for such an easy and cheap procedure how much of a difference it made. I personally paid my mechanic $70 to perform this service. Worth every penny. I hope this helps educate some people into getting the most out of their LS400.
cleaning the 'air mix path' as its known did great stuff for my engine, smoother idle and noticeably improved throttle response
avoiding repeated short trips i think is the best remedy for insuring everything stays fresh, as well as letting the car stretch its legs every now and then
I have been trying to share this information like the ECU capacitors issue but my limited English was not enough to explain the detail. 11 years ago, I had been positing about the fundamental LS400/Celsior's capacitor problem but most of people didn't pay attentions enough and almost disregarded me. But LScowboyLS understood me well and he gave me personal messages as well as requested me to talk on the phone. He quickly started a new thread and it became one of the biggest threads. After that, it was added to the FAQ page as a sticky.
I still find people who are suffering those low idle, rocket start and strange throttle response problems these days. I was thinking of asking some English/American native gentleman who has been experiencing those problems and succeeded to fix those actually. I found 400fanboy was the right person and actually he accepted my request and he wrote the detail adding his actual experience. Thank you very much for starting the new thread quickly. I think it would be better to add this to the FAQ page as a sticky. The FAQ page has a thread about the cleaning of the MAF and the throttle body but it is also very important to clean the air mix path. Do other moderators agree with me?
You know how our cars love to hang in 2nd gear in the first drive of the day? The buyer's guide has a line specifically about this:
On the first drive of the day, it will hang in 2nd gear up until around 2600 RPM even if you're easy on the throttle then slam into 3rd. Just once. Afterwards it will never do it again. All the 1UZ Lexuses I've driven do this and the consensus seems to be that it's normal and can be programmed out by changing some components in the valve body. TransGo sells a kit online for around 70$ IIRC.
4.5 years of ownership my car has acted EXACTLY like this. No deviations, always did it every single cold start.
Not anymore. It took me a minute to realize it, but it just hit me today. My car doesn't bang third anymore on the first start of the day. It shifts exactly the same as every single other shift it ever makes. I'm shocked.
Would love some other people to confirm this so I can add it to the list - it would be a ideal symptom to add to the list since it's universally understood.
My experience is different. Three different 98-00 LS400s have always carried second gear until I get out of the neighborhood. Sometimes sooner if the outside temp is hot, sometimes longer when it is real cold out. Before *and* after the air / mix passage cleaning.
My experience is different. Three different 98-00 LS400s have always carried second gear until I get out of the neighborhood. Sometimes sooner if the outside temp is hot, sometimes longer when it is real cold out. Before *and* after the air / mix passage cleaning.
Rich
Yeah, my 99' always shifts at 2750 RPM from 1-2 for the VERY first time, then drives normally after that.
I'll have to clean the air mix paths, did the throttle body cleaning when I first got the car back in Dec 2018 but never thought about the air mix holes above as my throttle response doesn't feel very quick when accelerating, like there's a lag. I'm thinking I might have a lot of carbon in there, so will likely use carb cleaner to get rid of that and see how it feels afterwards.
Yeah, my 99' always shifts at 2750 RPM from 1-2 for the VERY first time, then drives normally after that.
I'll have to clean the air mix paths, did the throttle body cleaning when I first got the car back in Dec 2018 but never thought about the air mix holes above as my throttle response doesn't feel very quick when accelerating, like there's a lag. I'm thinking I might have a lot of carbon in there, so will likely use carb cleaner to get rid of that and see how it feels afterwards.
You definitely need to clean those air mix passages including the injector's part where directional indexes are pointing. When the cleaning was not done for many years, badly clogged injectors can't be cleaned just using a spray can or 2. In that case you need to use an air compressor. Sometimes you have to clean injectors professionally removing them and using an ultra sonic cleaning machine.
You definitely need to clean those air mix passages including the injector's part where directional indexes are pointing. When the cleaning was not done for many years, badly clogged injectors can't be cleaned just using a spray can or 2. In that case you need to use an air compressor. Sometimes you have to clean injectors professionally removing them and using an ultra sonic cleaning machine.
How do you know, when you're using the spray can, when the passages are "clean"? What denotes them being free of carbon deposits?
How do you know, when you're using the spray can, when the passages are "clean"? What denotes them being free of carbon deposits?
A simple and easy way is just to drive the car and check that jerky acceleration is completely gone. As long as I have tried, unsuccessful cases were cars which have been in use of the low octane gasoline. Penny-wise and pound-foolish, you know.
Another way is to check the actual air flow which needs to rotate the crankshaft aiming to open intake valves and listen to the sound of air flow at the spark plug hole using a stethoscope. You have to do this 8 times to check all cylinders. The complete confirmation needs some extra time and efforts. As long as you have been in use of the high octane gasoline and you apply compressed air with one or two carbon cleaner cans, those passages are usually well cleaned.
if the coolant is still too cold for the gauge to move (under 100°F) then yea it'll hold 2nd until 2500 rpm only on the very 1st shift, and then never again until the next cold start... this has always been consistent without fail
My car used to be quite bad at hanging onto the gear, it would make it to 2500, even 3000rpm before slamming it home quite hard. The engine would actually "surge" in revs and over-rev during the gearshift like the transmission was slipping. It would go 2600, shift, 2750, 2000.
I've now driven the car a bunch and really been paying attention to that first shift after a cold start. The previous behavior is gone. It no longer hangs onto the 2-3 shift. The only service that was performed was the throttle body cleaning, the air mix passage cleaning and an engine oil change. That's it.
See the video I just recorded. We see two 2-3 shifts in the video. One at 0:58, one at 1:36. I gave both acceleration runs the same amount of throttle and both shifted at 2300 RPM. Both shifts felt identical from my driver's seat. 🤷♂️
The car has not been started or moved in 2 days with an ambient garage temperature of about 70 degrees fahrenheit:
So yeah. I have no idea what's going on here. The behavior that was supposed to be expected and seen in every LS... doesn't happen anymore in my car? Has anyone seen behavior like this before? I'm surprised to hear you guys having performed this service but still experience the hard shift.
P.s please forgive my abysmal fuel economy - I haven't been over 50mph or seen a highway with this tank of gas. Lots of sitting in heavy city traffic and 100 degree days running the air conditioning has truly tanked my fuel economy this summer.
for awhile i've had a 'theory' as to why it does this since you also get a good amount of engine braking if you let off before it shifts out of 2nd... it's so that the LS buyer will be able to better maintain control heading down their long luxurious driveway in the morning without the car continually upshifting and gaining speed lol
i'm sure this isn't even close but i chuckle thinking that it could be... after all this car is full of little hidden luxuries once you delve into the finer details
for awhile i've had a 'theory' as to why it does this since you also get a good amount of engine braking if you let off before it shifts out of 2nd... it's so that the LS buyer will be able to better maintain control heading down their long luxurious driveway in the morning without the car continually upshifting and gaining speed lol
So it's interesting you say this, I wonder if you're onto something.
I still experience the extra engine braking. It's *really* subtle, what it feels like is that the engine actually stays engaged in the gear instead of opening the clutch and allowing the torque converter or whatever to slip and the car to "coast" like it normally does when you let off at lower speeds. It feels far more like a manual transmission car with true, 1:1 engine braking rather than the "coast" the LS will typically do if you let off the throttle completely in a lower gear. I wonder if this is done to increase maneuverability after just having started the car. However, devils advocate here - if the purpose were maneuverability, why wouldn't this be done every time the car is started? Why is it only when the car is cold? This to me hints at a more mechanical purpose rather than a practical one. If I had to guess, it's probably something to do with oil pressures but I am just guessing. Without confirmation by the person who programmed it I guess we'll never know.
Also this being said: I still don't experience the harshness. There is slightly more engine braking, but it doesn't hold a gear longer than it should... the shift is not different once it occurs. It just... engine brakes a little bit harder, more like how it engine brakes in first gear all the time.
Now I'm really rambling. I'm sorry.
Originally Posted by Stroock639
i'm sure this isn't even close but i chuckle thinking that it could be... after all this car is full of little hidden luxuries once you delve into the finer details
My absolute favorite hidden luxury is the 3rd sun-shield visor above the rear view mirror.
I've owned the car for 4.5 years and it's been useful maybe two times for less than a minute each time. But I still get such joy out of it lol. I always point it out to my friends LOOK AT IT LOOK AT THIS HAVE YOU EVER SEEN THIS!?!?!! it's great.
So it's interesting you say this, I wonder if you're onto something.
I still experience the extra engine braking. It's *really* subtle, what it feels like is that the engine actually stays engaged in the gear instead of opening the clutch and allowing the torque converter or whatever to slip and the car to "coast" like it normally does when you let off at lower speeds. It feels far more like a manual transmission car with true, 1:1 engine braking rather than the "coast" the LS will typically do if you let off the throttle completely in a lower gear. I wonder if this is done to increase maneuverability after just having started the car. However, devils advocate here - if the purpose were maneuverability, why wouldn't this be done every time the car is started? Why is it only when the car is cold? This to me hints at a more mechanical purpose rather than a practical one. If I had to guess, it's probably something to do with oil pressures but I am just guessing. Without confirmation by the person who programmed it I guess we'll never know.
Also this being said: I still don't experience the harshness. There is slightly more engine braking, but it doesn't hold a gear longer than it should... the shift is not different once it occurs. It just... engine brakes a little bit harder, more like how it engine brakes in first gear all the time.
Now I'm really rambling. I'm sorry.
well in 'the theory', once they've left the driveway and safely made it to the handicapped spot at their orthopedist's office they've successfully avoided the possibility of the car accidentally rolling out into the street where a crash could be caused, and there's no longer a need to be extra cautious
again this is all just a silly idea of mine, i'm sure there's a mechanical purpose like helping warm up the fluids more quickly
Originally Posted by 400fanboy
My absolute favorite hidden luxury is the 3rd sun-shield visor above the rear view mirror.
I've owned the car for 4.5 years and it's been useful maybe two times for less than a minute each time. But I still get such joy out of it lol. I always point it out to my friends LOOK AT IT LOOK AT THIS HAVE YOU EVER SEEN THIS!?!?!! it's great.
getting to make make real use out of it is such a rare event i made sure to take a pic last time i got to haha
07-15-22, 05:05 PM
Jerky acceleration, Dokkan\rocket start: air mix passages\throttle body
