95/96 Ls400 Low Idle, Engine Dies And Jerking Thre

[95LS400Bob]

I am trying to make a thread here for the many of those with low idle, engine quits after an extended highway cruise when coming to a stop, and a mysterious drivetrain jerk when you let off the throttle and get back on....sometimes...and usually happening over 40 mph.

My 95 Ls400 built april of 95 which now has 150,000 miles has these problems.

I've done full diagnostics. I've gone after the throttle body and the Idle control valve. All of which were working perfectly. After 3 days of reading threads at several different forums of similar problems with 95's, several emails and follow ups on who found what the problem was and how solved I wanted to put all the information here so the next guy could find it easier.

Some guys are driving around with the a/c on to keep the engine running at a faster idle to keep the car from dying.

I'm convinced all 3 problems are related to the ECM and it's controlling of the idle air control. While there were a couple of TSB's on this it was never a recall. Those of us who bought used or have high miles are out of luck for any dealer help...at least I would think.

Your Ecm is located behind the glovebox on the passenger side. If you want to read what number Ecm you have..you can do that by not removing it. Just remove the lower plastic panel below the glovebox and look up in there. You'll see "Engine Computer Label" and the numbers.

For 1995's:

Your original Ecm is either:

89661-50220 or 89661-50221 if Federal (49 state). Lexus new replacement on the TSB says to replace with 89661-50224

If California then your orginal Ecm is either 89661-50230 or 89661-50231. The TSB calls for 89661-50234

But searching a local Lexus parts site shows that number has been replaced with 89661-50235-85.

The cost of these Ecm's new is just total crazy. But there might be another solution.

One member bought a used pcm from a wrecking yard #80661-50224. He paid about $150 for it and it solved his issues. I did some searching in wrecking yards and there are some of these #'s out there.

If you have a California car then there seems to be few out there. Mine is a California car. I don't know if a 49 state Ecm will work...I suspect it will...but unknown at this time.

Another member bought a remanufactured Ecm for his 49 state car. He paid $300. for it and it has a 1 year warranty. He also stated that it cured all problems. The company he purchased it from was Auto & Truck Electronics in West Palm beach, Florida. He said the part number was #95 Int 56834. (That was a 49 state unit).

There are other places on the web where rebuilt Ecu's are sold. The problem is most are listed by the old number. We have no way of knowing if the old units are rebuilt and then "reflashed" to the later specs which we are looking for to solve these issues.

I'll try to find out about that and post here what I find out.

For 1996's: The Ecm you want is 89661-50303. Original's were 89661-50302. A wrecking yard buddy did a nationwide search and there are used 89661-50303's out there. Evidently these work in all 50 state cars.

Ps: A 1996 Ecm will not work in a 95. It turns the check engine light on. That's been tried.

Update: I just received an email from the gentleman who bought the remanufactured pcm from Auto & Truck Electronics(mentioned above). He confirmed with them that the Ecu had the latest software upgrade before he bought the Ecu. He also commented the car shifted smoother than it ever did.

[bartkat]

I don't have one of those cars, but this is a great thread start and the info is interesting and helpful.

[95LS400Bob]

I bet I must have found near 20 people who had the problems..came in and made a couple posts and hadn't been heard from again. I contacted some by email and I learned a lot. A lot of peoples cars had the symptoms of all the problems but had trouble describing it. And much was confused by throttle body cleaning which solved a lot of Gen 1 problems but not Gen 2.

[99lsguy]

Bob,

Great info........... thanks for your research!!!

[VMF]

hey Bob, nice research:) my guess was correct and it is ECM:)

i do have low idle rpm but it doesnt happen on a regular basis and only after the engine was started after a night stay, if i rev the engine to 4-5k rpms after its been completely warmed up it usually solves the problem so i dont know if my low rpm relates to the ecu problem. do you have the low rpm and if you do when do you get it?

[95LS400Bob]

VMF you absolutely called it from the get go. :D The more I dug the more eveident it became that all the problems are ECU related.

My car will start up cold about 1400. Then taper down as it warms up to the normal 650 at idle. That shows all is fine.

But then at a stoplight...you might notice idling at 400 and that gets you to wondering. Then maybe later you are idling higher. Sometimes you catch the tachometer wavering slightly (engine is hunting for that idle speed). All is no big deal and many probably don't notice.

Then maybe you are driving along about 40 to 50 mph and get off the throttle for whatever reason...but just for second. When you step back on the throttle (just as you touch it) you feel this jerk or clunk. Hmm? What was that? So you go try to make it do it again. It doesn't. All is normal. So you disregard it.

The you take a trip on the freeway...maybe 60 miles down the road. You take the offramp and stop at the light. You look at the tach and you are idling 200 rpm. But the car is smooth and if it were not for the tach...you wouln't know.

Next stoplight you come to...it dies. You don't feel it but you see the lights on the dash all come on. You find neutral and the car starts right back up. Engine idle is the normal 650....smooth and steady...not a flicker on the tach needle.

You're glad nobody rear ended you and now you proceed with caution. But now it idles perfect every time. A few miles later..you might notice 500 rpm idle or the tachometer slightly adjusting. And the cycle repeats.

It never dies on you till you do a freeway jaunt.

The real mystery behind all this was we bought the car in the summer this year. It had a check engine light on but ran smooth as silk. The wife had to drive it back to Reno which was a 500 mile trip in a very unfamiliar car which needed suspension work(clunk real bad in the front end) so I was concerned for her. We stopped many times on the way home and the car never died once.

For the life of me....I could not figure out why it never died. Then in the research I found where many 95 owners were actually turning on the a/c when getting off the freeway. That steps up the idle and would keep it from dying. Sure enough...she had the a/c on the whole trip home. :P

My wife drives the car but never hits the freeway around here. So the car continues to run. But on the trip to Phoenix with no a/c on...the engine dying starts. Therefore the research hunt. I had even created a device that would keep the car running...was planning on doing a freeway jaunt and doing a roadside test to catch the idle control valve nearly closed (which is what is causing the engine to die). But that is not necessary now as the research paid off and I am convinced it is an ECU problem.

One member has offered their old Ecu (49 state) to see if it would work in my California car. I just may try that as a test...just to see if it is compatable with my car. If it is, then I will hunt me a 49 state federal pcm #80661-50224.

The research also pointed out one troubling fact....Lexus knew about this. Yet no recall. Those people that have 70,000 miles or close can probably raise a stink at Lexus and get fixed...maybe with little money. But those of us with high mileage and a now a 10 year old car have to bite the bullet. Maybe unless you are an attorney. <_<

Update: Courtesy of a fellow member here, I have a 49 state ECU coming to test to see if compatable with my California car. That will be interesting.

[VMF]

weird, i have the same idle problem but it just doesnt die on me... yet....

half a year ago i noticed the idle problem just like u descibed, when i start the car engine has like 1400-1500 rpms and when it cools down it drops to 600, but agter i drive the car for a few mins the idle drops to 400, it doesnt matter if the tranny is in P or D but after revving the engine it goes away, but not always. i didnt really pay much attention since it is not causing any real trouble to me but if it will lead to the dying problem i should start to get worried right about now, i will check the numbers on my ECM on next weekend, too lazy and too cold to do it after work:)

[95LS400Bob]

You should have a "302" unless it has been changed. "303" is what you want. And I have some spotted in wrecking yards. I even have a 303 spotted in New York. :D

Do you get that occasional "jerk"? Not sure if 96's had as much problem with it.

[VMF]

nah, no probs with jerking so far, i mean it jerks but rarely and i think its due to dirty fluid, dont have time to change now.

[95LS400Bob]

Performing a little test here swapping Ecu's. My 1995 original pcm is a 89661-50231 (california) has been removed and in it's place is a test unit 89661-50221 (49 state ecu) from a member's car.

Purpose of this is:

1.) Can a 49 state ecu be put in a Califirnia car with no problems?

2.) Does the 49 state ecu have more power and better throttle response?

3.) Since my car has the stalling after 20 min or more of highway speed....will this Ecu solve that problem.

4.) Are there any noticeable issues regarding shifting, idling and performance with this Ecu over my (suspected bad) Ecu?

I installed the 49 state ecu and no check engine light...no obvious problems. I thought the car had more power. I told the wife to take it for a little spin and she said it definately has more power.

That's all we know at this point. A few more days of driving and the wife testing(this is her car...I seldom drive it) and then a 120 mile road trip to see if the car stalls. I'll report back.

[cowwboys]

Gentlemen, I do not have the stopping or jerking problem. But, my car idles at an AMAZING 100-200 RPMS . I am baffled! What in the world is going on! I am planning on cleaning the throttle body one day this week to see if it fixes the problem. Should I look into changing the Ecu as well?

[95LS400Bob]

My guess would be this. If the car does the normal fast idle when cold...then tapers down in idle speed...that shows the IAC is working. If you have a 100 to 200 rpm idle all the time...I would look at the IAC valve to be sure it is working. If you are getting normal cold start rpm's, then normal 650 to 700 idle..but later in the day are seeing 100 to 200 rpm....I suspect the ECU.

Least that is my opinion so far with these tests.

[VBdenny]

Excellent and very detailed information there Bob. My car runs at 1600 RPM's on start up, and slowly drops in increments until warm idle at 600 RPM's. The car has never stalled or even felt like it might. When I first bought the car I was concerned about the high start up idle speed, but I believe that 1600 RPM's is normal on a 1990.

[95LS400Bob]

It seems to be a 95 and 96 "thing" with the ecu's near as I can figure. Seems a lot of guys did have some idling problems with the earlier cars and cleaning throttle body cured it. But seems I didn't find anyone with a Gen 1 that would do this stalling thing after 20 or 30 minutes on the highway. Have to do a road test on this ecu to see if it stalls or not. Then we will know more.

[95LS400Bob]

Here's the results after a 70 mile run at 80 mph non stop.

Be sure to read the entire thread. These are the results of replacing my Calif ecu 89661-50231 with a 49 state ecu 89661-50221.

The car idles 600 rpm..absolute steady..not a waver on the tach. Even after the sustained highway driving (it used to die at idle.) This proves my problem was the ecu.

The car has much better power everywhere from stoplight to stoplight or accelerating on the highway. This shows the Cali ecu's are as suspected...cut back on engine performance.

The jerking that happened when closing the throttle and then getting back on the throttle at around 45 mph has only occured once with the 49 state ecu and it was nowhere near as harsh.

So I will now return this borrowed ecu and hunt down a 49 state unit and install it in my car...or will go for the "improved" ecu if I find one at a reasonable price.

Hope this helps someone in the future.

[pgupta]

VMF you absolutely called it from the get go.  :D  The more I dug the more eveident it became that all the problems are ECU related.

My car will start up cold about 1400. Then taper down as it warms up to the normal 650 at idle. That shows all is fine.

But then at a stoplight...you might notice idling at 400 and that gets you to wondering. Then maybe later you are idling higher. Sometimes you catch the tachometer wavering slightly (engine is hunting for that idle speed). All is no big deal and many probably don't notice.

Then maybe you are driving along about 40 to 50 mph and get off the throttle for whatever reason...but just for second. When you step back on the throttle (just as you touch it) you feel this jerk or clunk. Hmm? What was that? So you go try to make it do it again. It doesn't. All is normal.  So you disregard it.

The you take a trip on the freeway...maybe 60 miles down the road. You take the offramp and stop at the light. You look at the tach and you are idling 200 rpm. But the car is smooth and if it were not for the tach...you wouln't know.

Next stoplight you come to...it dies.    You don't feel it but you see the lights on the dash all come on.  You find neutral and the car starts right back up. Engine idle is the normal 650....smooth and steady...not a flicker on the tach needle. 

You're glad nobody rear ended you and now you proceed with caution. But now it idles perfect every time. A few miles later..you might notice 500 rpm idle or the tachometer slightly adjusting.  And the cycle repeats.

It never dies on you till you do a freeway jaunt.

The real mystery behind all this was we bought the car in the summer this year. It had a check engine light on but ran smooth as silk. The wife had to drive it back to Reno which was a 500 mile trip in a very unfamiliar car which needed suspension work(clunk real bad in the front end) so I was concerned for her. We stopped many times on the way home and the car never died once.

For the life of me....I could not figure out why it never died. Then in the research I found where many 95 owners were actually turning on the a/c when getting off the freeway. That steps up the idle and would keep it from dying. Sure enough...she had the a/c on the whole trip home. :P

←

How about a ditto on my car. Reading your post seems like you are reporting my problem. Just died on me this morning on the same off ramp from the freeway to work - only for the 10th time in the year because I purposely shut off the "AUTO" to kill the A/c and lo and behold I was on the side of the road with my flashers on trying to restart the car. Every bit else is identical - start at 1100+ rpm, settles to 650, dies after a long cruise, jerks at 40/45 or even at idle, hesitation when accelerating but only once in a while. There is no true pattern to the jerks or the hesitation during acceleration - thats what makes it so hard to pinpoint the problem.

Here is the odd part in your data chain.... mine is 94LS400.

Help me! How do I get to the ECU? any pics to help me out?

[95LS400Bob]

Disconnect the battery cable first. Important.

The Ecu is located under the dash on the right side behind the glovebox. Remove the bolts and take out the glovebox and the lower cover panel. Look up in there and you will see the ecu. It's the large box with 4 big plug in leads. Just unplug the leads and remove the bolts to take it out.

The number on the ecu is like 89661-50141. There was more than one ecu for 1994. The latest shown I could find was a 89661-50142. There is some interchange between 94 and earlier cars on the ecu. Not so with 95.

You can do one of the rebuilt deals or take your chances at a wrecking yard. I would do a 89661-50142.

You're the first to have a 94 with all the identical symptoms that I know of. Most guys with earlier models cleaned the throttle body or replaced the idle control and solved the problem. But most of them had idle problems all the time...not this highway cruise and die deal like you got.

[iatimlee]

Here's the results after a 70 mile run at 80 mph non stop.

Be sure to read the entire thread. These are the results of replacing my Calif ecu 89661-50231 with a 49 state ecu 89661-50221.

The car idles 600 rpm..absolute steady..not a waver on the tach. Even after the sustained highway driving (it used to die at idle.) This proves my problem was the ecu.

The car has much better power everywhere from stoplight to stoplight or accelerating on the highway. This shows the Cali ecu's are as suspected...cut back on engine performance.

The jerking that happened when closing the throttle and then getting back on the throttle at around 45 mph has only occured once with the 49 state ecu and it was nowhere near as harsh.

So I will now return this borrowed ecu and hunt down a 49 state unit and install it in my car...or will go for the "improved" ecu if I find one at a reasonable price.

Hope this helps someone in the future.

←

Awesome information Bob!! I am one of those 20 guys you mentioned that had posted a question, heard nothing and moved on because I thought I was the only one. This is exactly what is happening to my '95 LS400. It started at around 100,000 miles and has got progressively worse. Two days ago, the check engine light came on after 10 minutes of highway driving speeds and now will not go off. I've got everyone of the symptoms you've described - low idle speed leading to stall after highway driving, jerking/clunking when letting off and then back into the accelerator when someone cuts me off, etc... I'll be looking for a new ECU and I'll post the results of my replacement when I get it completed.

I just wanted to say thanks not only for doing the research but posting in such detail. The info here is VERY valuable and I'm going to ask my wife for a GOLD membership for Christmas.

Thanks again!

[95LS400Bob]

To the top.

[95LEX400]

I had the exact same problem and the info I gathered here and on another Forum was invaluable. Thanks!

I hate it when someone solves there problem and doesn't let anyone else know. so here's my "Problem solved" post...

I got the car back today. It runs great and no hint of the stalling problem after prolonged freeway drives or the jerking during throttle tip in at cruise after extensive testing by the dealership and myself. They ended up replacing the ECU after trying a few other things that didn't work. I originally also had an additional high RPM miss that was fixed by changing the sparkplugs. The dealership even delivered the car 75 miles to my house and drove the loaner back.

It might cost a little more to get a clean used Lexus from the dealership but in my case it really paid off. They really stand behind these cars and have gained a loyal customer for any future Lexus purchases. If anyone is in the market for a used Lexus call Larry Gentry at the Lexus Store of Lexington 859-621-0391.

Sorry for the shameless plug but these guys really came through for me.

[highlander]

I got the same problem.. guess i'll be looking for a ECU of these./

[sonnyblue]

My 95 LS400 is having the throtle jerking problem. At above 40mph, if I take my foot off the gas pedal quickly, I feel the whole car shaking and jerking. Would replacing the ECU fix this problem? Do I need to know exactly what my ECU number is before I order it from Auto Truck in Florida? Thanx.

[95LS400Bob]

89661-50234 is supposed to fix the jerk problem. 2 members I contacted said it fixed the problem.

However, the number on ecu from Auto Truck in Florida may be a different number all together. Probably their number 56834. Which one member got and it must have had the latest upograde because it fixed his problem with the jerking.

[pgupta]

You're the first to have a 94 with all the identical symptoms that I know of. Most guys with earlier models cleaned the throttle body or replaced the idle control and solved the problem.

==================

Was waiting for the weather to clear up and attempt the throttle clean up as the first step before hitting at the ECU. I found major carbon deposit on the inside. Using a household oven cleaner, I patiently dissolved all the hardened carbon deposit on the valve disk. Now when the valve disk is fully closed, I can see a nice clean clearance gap for the air to flow through at idle. I suppose this was the reason for the engine dying after a long haul.

I notice my cold start idle speed went up slightly - 1100 rpm from 800rpm previously. I tried getting off the ramp with A/C off - no dying this time! Will see if I can keep repeating this test and never fail.

My reasoning - there appear to be 3 cables keeping that valve open - cruise control, accelerator and perhaps idle control for cold start. So after a long haul, when getting off the freeway, none of the three cables are pulling on the valve to increase its opening and you need that minute clearance to sustain the air flow for idling the engine. With carbon deposits blocking it, no wonder the engine was choking and dying.

Now I need to deal with the hesitation at 45 mpg when accelerating uphill. That obviously has nothing to do with the throttle body cleanup as at 45 mph, the valve disk is open quite a ways.

[sonnyblue]

Bob, well, it finally happened to me. I was driving a long 3 hours trip from Austin to Houston on my 95 LS and when I got off ramp, the engine just quit like you described. I never experienced this problem before, maybe because, I just guess here, that I had always shifted to the 3rd gear to slow down the car and therefore accidentally ramping up the rpm - avoiding the ECU problem?!

This situation is quite dangerous that I think Lexus should do a recall on it. I will attempt to talk to Lexus dealership this week to see if they can fix it free for me. If not, I may have to send a letter to Lexus regional or national customer care general manager. Can you imagine how many senior drivers would handle this situation without going panic and causing accidents?

Again, you are doing a great service for all of us here! Thanks mucho!