On heavy acceleration from stop, my car will often decelerate dramatically at shift from first to second gear. So when starting off the line it's accelerate -> decelerate -> accelerate.

Dealer says that there is no fix for this, and that there is only one version of engine control module for this model, but they also WON'T say that "all of them do this."

I'm suspicious.

The problem is so offensive that I've taken to shifting manually, which does completely eliminate it.

My attitude is colored by the fact that my new 1990 LS400 had a very annoying problem that was ultimately fixed by new ECM, but I don't think that the availability of that fix was ever publically acknowledged. So only the owners who complained long enough got the fix.

Can anyone shed some light on this subject?

Thanks.

[By the way, I drove an LS430 and tried hard to get it to show some hint of this problem, and it didn't, so obviously Lexus engineers have found a way to solve it!]

[Another thought: I understand that owners of early 1999 GS400's have reported a problem similar to this, which was fixed by ECM swapout, and it occurs to me that the dealer may have dealt with an unhappy camper by swapping out the ECM from my car when it was in inventory. Can GS400 and LS400 use same ECM?]

 

I also had a 1990 LS 400 and never experienced the problem you described. It was strong from the get go without a trace of hesitation. I think YOUR Lexus has the problem. Have you tried another dealership to diagnose the problem?

 

I'm sorry I didn't make myself clear. It is my 1999 LS400 that has the acceleration/deceleration problem. My 1990 never showed any sign of that kind of problem.

The problem that my 1990 LS400 had when I took delivery of it in Feb. 1990, was that when you were descending a steep hill and holding a constant speed, where engine braking was needed, it would go into an alarming "bucking," jerking oscillation. Eventually they did come out with a fix for that. Actually, it fixed it about 95%. Two of my friends got 1991 LS400's and after I described it to them they also determined that if you observed very closely you could see a remnant of the phenomenon in their cars as well. But Lexus did fix it sufficiently that no further complaint was warranted. People who usually drive in relatively flat terrain probably wouldn't ever experience it.

My 1990 model was manufactured in November of 1989. I don't know how many cars got to the U.S. with the problem, but it was startling when it did occur.

No, as yet I have not spoken to other dealers about the problem with my 1999 car. It is a long drive to get to Lexus dealers from where I live, and the car is not driven on a daily basis. Hopefully, some member of this forum will give me some information that I can use when attempting an intelligent conversation with the next one I try!

 

My 98 had a hesitation aort of like that at startoff when I took delivery in March 98, and still does sometimes. I was told it had to do with the throttle by wire system, and that in the LS430 it was eliminated. They told me that as it learned my driving style it would go away, and it has for the most part. It only happens sometimes when its in normal and not ECT PWR mode.

 

Go to the dealer and test drive another 99. If it doesn't have the problem have a service technician ride with you in BOTH cars. If the dealer won't help you, report their sorry operation directly to Lexus.

 

Thanks for response, Stephen. I believe we are talking about the same "issue," as they say. I too was told that this performance oddity has to do with the "throttle by wire" system, as if somehow I should be overjoyed that there is such advanced technology between the accelerator pedal and the engine.

And I too have noticed that using the ETC PWR mode does improve things considerably. But if you want to get serious in dealing with the guy in the adjacent lane you will shift manually all the way up from L!

This crapola seems to have come along with the introduction of the 5-speed transmission.

It will learn my driving style, huh? What if half the time that the car is driven it is being driven by a different driver who has a completely different style? I don't seem to be able to locate the control where you tell it which driver is at the wheel - or are the designers so clever that the ECM is affected by the seat selection buttons? Wouldn't that be a hoot ...

One of these days I'll get up the motivation to make a list of some of the other oddities of my car, and post for the consumption of members of this forum, just in case I can establish that one or two of them actually have fixes. The only one that seems to be addressed by TSB is the squeal and roughness when the steering wheel tilt is motoring downward. But I know that there can be campaigns that don't show up in a TSB.

When it comes to dealing with the service departments of car dealers, I have found that the only way to get good answers is to already know the answer. Just asking very good questions isn't good enough.

The LS400 approaches perfection more closely than other cars that I have evaluated, in some cases by A LOT, but it still isn't perfect.

 

Interesting suggestion. However, I think that I would have a much stronger negotiating position if I could cite a specific case where another car with the same problem actually got it fixed. And state exactly what they did to fix it. Otherwise, I'm afraid that they would say that the problem is "within the normal range of variability." In fact, more or less that is what the dealer has already told me, in which case it would do no good to show them another 1999 LS that did not exhibit the problem.

My brother has a 2000 GS400 with a lot bigger, more aggravating problem than this one, and he has been given that type of runaround by the folks in Torrance.

 

Yes my convo with the service department about a week after I took delivery consisted of this.

Me: I'm having a problem with my new LS400, I seem to get a pronounced hesitation at takeoff, not smooth at all

Them: Is this your first LS?

Me: Yes it is

Them: Its normal, try driving in ECT PWR and once the ECU learns your driving style it will go away

Me:Uh, okay

I had a thhought, maybe replacing the ECU with an aftermarket unit would totally remove the problem.

I've had no other issues except the fact that the cupholders are useless and the Lexus phone sucks (deactivated it, I use my cell phone and a $60 cigarette lighter mount from Best Buy and it works better than the $2500 phone ever did). What are your other concerns? My car has been flawless.

 

I'll post my other concerns as a new thread. Maybe we can entice some more owners to show themselves!

 

I've got a 93 LS400 and I think I've got a comparable problem to yours Stephen. When accelerating the shifting is not at all smooth. It feels like the car cuts power when it shifts up. I have to lay off the gas and then if I hit it again I've got the power back. But like I say it typically hesitates. I mostly drive the car in power ECT mode but I've noticed that when I start experiencing this lacking performance, if I switch back to normal mode the car works well again. After driving in normal mode for a while the car starts acting up again. Switching back to power mode helps this. It's as if the car is doing a very poor job of attenuating for driving style.

One very interesting thing; I was experiencing this problem quite a bit for awhile. One night my battery died on me. It was old and coroded and really needed to be replaced. After being stranded at a gas station and making a late night trip to Sears, I replaced the battery. Immediately I noticed a significant improvement in performance. About a month later I started experiencing the performance problem again. I finally got around to cleaning the coroded battery terminals; I disconnected the battery, cleaned the terminals, and once again I noticed a significant increase in performance.

It seems as though the car is doing a poor job of sensing driving style. It's almost as if each time I disconnect the battery, the ECU resets itself and I get the kick that I'm looking for. But after driving for a while the car gets goofy again. I really hate to have to disconnect the battery every few weeks but until I find a real fix this might be what I'll have to do. Maybe the Swift Racing Intake/ECU combo will solve this but we'll have to see.

P.S. Does anyone know if adjusting the throttle cable would improve this problem. It's time for that sort of maintenance including valve shim adjustment.

Thanks for your help.