Hi, PureDrifter ... if you needed to get an ECM / ECU rebuilt ... who comes to your mind ... anyone in particular?

Tanin auto is a well respected vendor here, https://www.taninautoelectronix.com.

I've got a local shop to me that specializes in all toyota/lexus performance (mostly 1/2JZ engines, high horsepower supras, etc...) that has been doing ECU cap replacement and repair for 10-15 years, www.driftmotion.com (1UZ ecu repair: http://www.driftmotion.com/1UZ-ECU-C...e-p/dm1676.htm )
Others have posted reviews for them as well, including for the LS400. https://www.google.com/search?q=drif....clublexus.com

You are welcome. I think the post below might help you some more.
A post by MngreLMatt 3 years ago

Yamae- Looks like the upper intake you're showing is the 98 & up so does the older one also have these larger air holes? I can't quite picture what the air mix path from the fuel injector's cross-sectioned diagram you showed above. When you mentioned using the carbon cleaner to clean the fuel injectors, are you talking about cleaning them while they're still attached or with them removed from the engine? Both of my 97 & 00 LS400's are in tip top shape but I'm curious so please elaborate on that. Thanks.

I believe he is referring to cleaning the air mix path with carbon cleaner, because it's essentially connected to the vacuum part of the injectors. Injectors wouldn't need to be removed unless they're really bad.

I don't think your 97 has an air mix path, but your 00 definitely does

Scraape- Yeah, I have my 97 for 20 years so have done lots of maintenance works on it. If it has the air mix path for the injectors, I would have seen it by now. Thanks.

Vacuum leak
 

Update:

So I got my car back after having the throttle body replaced, and I still had the low idle. I messed around with the throttle position sensor again, this time I kept the engine running. In park with the engine on I brought it up to 950 and tightened the screws. In drive it now sits at 650+-, way better than 400 were it was prior. So far it has been steady with stop and go bay area traffic. Maybe give that a try for the people still having issues?

Update
 

Hi everyone,

Apologies for the slow response.

I haven’t been able to pursue this matter further as I have been far too busy with work and school.

At this point I’m almost 100% sure it’s the ECU that’s causing the problem. Also, in the next couple of weeks in Southern California, air conditioning will become more of a normal occurrence so the issue will be somewhat less prevalent.

Thank you Puredrifter for the ECU repair recommendations. That will be my next approach when time permits.

My 1999 LS400 had one occurence with extremely low idle to the point of stalling...it happened only once but once was too much so waited a few months to see if it happened again.

Today I replaced both VVTi solenoids or Oil Control Valves (OCV).

I did so without disconnecting negative battery cable to avoid ECU reset therby only one variable...new OCV's

Changed when engine was warm to better compare results.

The idle was smoother and at a slightly higher RPM in park.

The OCV is an electromechanical devices with a pintle that wears in it's bore with a return spring that has probably grown tired after 20 years.

On information the new OCV is better designed yet "Made in Mexico" does not inspire the same confidence as "Made in Japan"

My 1999 LS400 had one bout with extremely low idle to the point of stalling...it happened only once but once was too much so waited a few months for a reoccurence.

Today I replaced both VVTi solenoids or Oil Control Valves (OCV).

I did so without disconnecting negative battery cable to avoid ECU reset therby only one variable...new OCV's...OEM parts.

Changed when engine was warm to better compare results.

The resulting dle was noticeably smoother with slightly higher RPM in park.

The OCV is an electromechanical devices with a pintle that wears in it's bore with a return spring that has probably grown tired after 20 years.

On information the new OCV is better designed yet "Made in Mexico" does not inspire the same confidence as "Made in Japan"

Thanks for sharing.

Yes, VVT parts can easily cause idle problems on any model of car when worn or faulty. My car is a 1996 however and therefore does not have a VVT equipped engine.

YODAONE - did your check engine light come on and thats why you replaced your VVTI control valve? My car is acting up again, was working fine, but now low. Might try replacing the VVTi valve like you and pray it works.

You can try cleaning the OCV first. When they fail you'll get misfires/extremely rough idle (think a cammed V8) whenever VVTi gets activated, among other things including stalling after high RPM.

No engine light....but after 170k miles, surmised thie pintle and bore of these valves were worn.

They fail.~ 200k so with the low idle question determined to replace both.

Have read the new OCV's are improved...perhaps someone can elaborate on whether or how so.

What's the RPM in neutral/park. 400 in drive can be just fine. There's no factory idle RPM designated for when the car is in gear.
https://www.clublexus.com/forums/sho...3&postcount=24

My 99 does 400 rpm idling in drive and sometimes it can be a problem.
In the summer heat in Phoenix I get battery lights / voltage drop (~10.5V) issues. No such issues in neutral/park, 700rpm (~13.5V), where I wish it would stay while in drive.
Also, again at idle in drive 400rpm there is a slight yet noticeable vibration and rumble throughout the chassis, low rpm harmonics... Up at 700rpm its smooth and quiet as new.

need help
 

my 1996 lexus ls 400 is throwing misfire codes and system running lean also the car is missing badly burning fuel and smoking horribly i have no idea what this issue is we have replaced the tps / the sparkplugs and wires as well as the coolant temp sensor the code also is random misfire all 8 cylinders i am at the end of my rope with this car could it be the o2 sensors?

Random misfires are often caused by the failing ECU.
You can simply check it measuring the AC ripple level.

Hi ... my gut feeling would be to check the ECU ( I tend to call it an ECM ) ... this is the computer box that controls the engine ( located behind the glove box if I am not mistaken ) ... at this stage of life, the capacitors inside the ECM tend to break down and begin to leak onto the circuit board ... thus causing weird problems exactly as you are describing. There is much discussion about this topic ... and there are people who rebuild these electronic units really well .... I know I that need to do mine and the last time I looked it was about $300 bucks or so to do this job ....

From what I have read, it should be very easy to remove the ECU yourself and send it in to a rebuilder ..... also ... I have read that it is possible to pull the top cover of the ECU off and take a look inside to see what is really going on ... any capacitors that are leaking should be quite obvious ..... there should be photos elsewhere here on this forum that show what to look for .. .. ..

I hope this helps ... and I hope your LS is back on the road again quickly and running well once again .....

1998 1999 2000 ls400 cleaning air mix paths
 

Yamae shared a link to a Japanese language website providing images and technique for cleaning injector air mix paths.

https://minkara.carview.co.jp/smart/...0193/note.aspx

Following are images and English translation:

https://cimg1.ibsrv.net/gimg/www.clu...106e0c4e99.jpg
Air mix path cover plate

https://cimg4.ibsrv.net/gimg/www.clu...b8064de034.jpg
Air mix coverplate removed
https://cimg1.ibsrv.net/gimg/www.clu...418b71fb2f.jpg
"Drive Joy" air mix path cleaner inserted into one of two large air mix path holes..
https://cimg1.ibsrv.net/gimg/www.clu...8c9f8ec978.jpg
..and the second large hole

One of the weaknesses of the 1UZ-FE engine equipped with VVT-i is low idling and instability. To make matters worse, this condition causes abnormal AT shifts and causes a docking start problem. Some people said that the AT was judged to be bad, and they replaced it but did not fix it.

There is no particular problem for several years from the new car, but since there is no idle port and idle control is performed only with the throttle valve, the area around this valve and the air assist system are contaminated with carbon etc., and the ECU can be controlled. If it goes out of the category, it will be out of range, and the idling will drop and be disturbed immediately. In particular, the air assist system under the lid fixed with two + screws, which is shown near the center of this photo, gets dirty, and when it reaches the injector, the idling is disturbed and the engine buzzes. It also becomes. If you do not clean this area as well as the throttle body, the engine will not be in good condition. Recently, I tried cleaning my car for the first time in a long time, but I'm feeling better.

When you remove the lid, you can see two thick holes and nine small holes like this. Below the nine holes is the throttle body, and the air weighed through these holes is taken in. The larger hole on the left is connected to the four injectors in the right bank, and air is sent 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, but since the engine speed slows down, it is necessary to spray with the right hand and control the slot link with the left hand so that the engine does not stop. Sometimes it is effective to blow this hole with an air compressor. The point is that the carbon that is clogged in the system is forcibly pushed 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.

The link I've introduced is about an American LS400 owner who was suffering from this problem, but there were a number of people who were in trouble, and I was very happy to help.

I first cleaned this line almost 10 years ago, but since then, my neighbor Celsior owner has been having trouble with the same problem, and 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. With the exception of one car, not only was the idling stable and the 750 rpm was perfect, but the car was in very good condition, especially the acceleration immediately after decelerating to the point of stopping was very smooth and pleased. .. 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.

If you are having trouble with the following symptoms, not only the throttle body was cleaned, but also the air assist system was cleaned. As I have seen people who were surprised at the improvement, I should have posted this earlier in Japan as well.

● Low idling
● Unstable idling
● Abnormal

acceleration after deceleration just before stopping (Doccan start) Even if you try to accelerate after a large deceleration at a tight corner, the speed does not increase and you feel that the gears are not connected. After that, if you have a symptom of sudden acceleration, it is recommended that you clean this area as well as the throttle body. After cleaning, it is necessary to remove the negative terminal of the battery, erase the learning data up to that point, and relearn. By the way, about half of the cars I've done so far had to apply a pressure of about 2 kg / square cm (28 PSI) with an air compressor. This is because the negative pressure of the intake manifold alone may not be enough to remove the carbon dirt that has clogged the air assist port of the injector.

Also, when the engine is stopped, there is a risk of causing a liquid hammer phenomenon, so be sure to do it in the idling state.

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