[hurricane]

I read an old review of the IS300 and the reviewer said that the IS300 has a drive-by-wire (electronically controlled) throttle (this may be old to news to some of you). He said that this is the reason that the IS feels like it has more horsepower than it does. It seems that if, for instance, you pressed the peddle in an inch, you would get the same rate of acceleration on a level road as you would going up a hill. Does anyone know the advantages of the electronically controlled throttle in more detail?

[This message has been edited by hurricane (edited December 18, 2000).]

 

[TEG]

Yes, the IS300 has "eThrottle".
The pedal is connected to a (traditional) cable that goes to the throttle body, but the throttle body is special in that the cable pulls on a sensor and an electronically controlled butterfly valve controls airflow to the engine.

Advantages:

1> They can use an ECU to tune throttle "tip in" so that (as you said) the car can feel more powerful and can have consitent pedal feel even if the ECU decides to give more throttle when going up hill.

2> It is part of the traction control system so the ECUs can reduce throttle (regardless of pedal position) if they detect wheelspin.

3> With an autotrans, the ECUs can make smoother shifts by adjusting throttle settings during the shifts.

4> Better control of idle RPMs for things like engine warmup, airconditioner load compensation, etc...


Disadvantages:

1> A (very) slight delay between your (pedal) input and the engine response.

2> Another thing that can break.

3> A disconcerting feeling that the car really isn't under your complete control.

 

[hurricane]

Thanks for the info TEG. I heard that there is talk about an electronically controlled steering mechanism. You could do some neat thing with this like changing the steering responsiveness at different speeds, emergency control compensation. But as you said then you would really feel out of control in your car. Imagine having your steering wheel stop working...

 

[Mustard]

So is this why the car sometimes feels like the throttle is being cut off when you go around a sharp fast corner? This is one of the few major criticisms of the car! In fact I'm quite surprised that it's not a major gripe on this board.

[From TEG: As far as I can tell, YES, this is why. I think the Lexus engineers did this on purpose to make the car more smooth and easier on the transmission. My theory is that the transmission control ECU says - "0I want to shift gears now", so the eThrottle ECU says "OK - I will not open the throttle until you are ready with the new gear". A typical (non eThrottle) car would start revving once you hit the gas, but if it needed a different gear then the car would "lurch forward" (which is what we are used to having happen)... It probably does help the torque converter/transmission reliability to avoid this "lurch" condition, but it is *VERY* disconcerting to feel like your car has *NO* power when you want it most.]




[This message has been edited by TEG (edited December 19, 2000).]

 

[hurricane]

Mustard,
I'm not sure if this is the cause of the cutout around corners. I've been wondering if the cutout is caused by the shift from first to second gear. The car will shift from first to second VERY early unless you give it alot of gas. There is a noticable pause when the shift occurs. Just a theory. Any other explanations (i.e. does if have something to do with TRAC or LSD)?

 

[Daniel]

are you sure you are not engaging the TRAC? Try running with TRAC off, I bet the delay will go away.

[From TEG:
My TRAC is *always* off, yet I still have the "dead time" sometimes when trying to hit the gas at slow speeds. When the traction control kicks in it has a similar sort of "I am not going to do that" sensation, but I can tell you for sure that the car does it sometimes even with TRAC off.
]


[This message has been edited by TEG (edited December 19, 2000).]

 

[Mustard]

Well right now the roads are all snow and slush covered, and I'm going around the corners very slowly even with the snow tires on.

But really, we shouldn't have to turn off the traction control system so that we can drive at normal speed on dry pavement. This is a problem if you ask me. If it's the TRAC doing it, then the TRAC is the problem. It really needs to be fixed.

 

[s0yb0mb]

Please explain to me how this is a *problem*.
The TRAC is there in case too much power goes to the rear wheels, which on a slick road would be pretty dangerous, causing the rear to break free. If the road is dry, push the TRAC button and turn it off and you'll have all the horses to play with. If it wasn't automatically on when you started the car, too many morons (myself included) would wreck their cars on an icy road. It's good logic to have it on by default.

Originally posted by Mustard:
Well right now the roads are all snow and slush covered, and I'm going around the corners very slowly even with the snow tires on.

But really, we shouldn't have to turn off the traction control system so that we can drive at normal speed on dry pavement. This is a problem if you ask me. If it's the TRAC doing it, then the TRAC is the problem. It really needs to be fixed.

------------------
~soybomb~

 

[TEG]

The "gripe" many of us have is that (even with traction control turned off) the IS300 will sometimes feel "dead" to throttle inputs when coasting along at low speeds. Some people say it happens more when going around corners, but I have had it happen even when going in a straight line.

My theory is that the eThrottle refuses to open when the transmission control computer decides it is a good time to shift gears.

Lets say you are coasting to a stop in 3rd gear, and then you hit the pedal to the floor. A typical (older) car would immediately start revving the engine (throttle open/more power) just as the transmission starts "kicking down" to 2nd or 1st. We are used to this as the (engine) sound increases and then the car lurches forward once the new gear is engaged. My guess is that the Lexus engineers decided that the "lurch" was a bad thing - it makes the car less smooth, and is hard on the drivetrain. So - they intentionally programmed it to avoid this by delaying the eThrottle response. Unfortunately the delay comes at a bad time (right when you want to GO GO GO), and it can last long enough to be downright scary at times. If they were able to make it happen in under 1/4 sec maybe we would never have started complaining. I think it could be possible for Lexus to reprogram some ECU code in existing IS300s to "improve" this issue for us, but they would have to make the decision to do so.

 

[TEG]

BTW: This never seems to be a problem if you come to a complete stop. My guess is that the transmission ECU has some logic like: "If (stopped) then (select 1st gear)."

If they revised it to say "If (under 10mph) then (shift to 1st gear)" it might make us aggressive drivers much more happy.

I would like it if the IS300 had an "auto downshift" button that did automatic engine braking (and anticipatory gear selection) as you coasted toward a stop.

 

[TEG]

Also, I just read an article about some new computer controlled braking coming out on high end Mercedes Benzs. It is supposed to (eventually) show up on all their models.

I don't remember all the features, but it was extensive -

like -

1> The basic electronic brake force distribution which varies front/rear portioning based on decceleration (unlike the old "fixed" portioning valves) [The IS300 has this].

2> Side to side brake force distribution which changes bias when braking around a corner.

3> The system can discretely apply the brakes lightly to keep the discs dry when driving in the rain.

4> A "soft" mode that makes the car stop more smoothly in stop and go traffic.

5> "Electronic Crumple Zone" where the brakes are applied if laser/radar/sonar (whatever) detects an imminent front end collision.
(What next - automatic full throttle if you are about to be rear-ended).

6> etc, etc.

Anyways - my point is that the manufacturers are in the process of giving more and more control of the driving over to computers.

Many of these new "features" have really good ideas in safety and comfort improvement...

*BUT* us drivers used to more manual controls will freak out when we feel like the car is not doing exactly what we asked it to do.

Once we all start learning to use these "features" it will feel unsafe to drive an older car that doesn't have all the computer aids.

For instance, many of us are getting used to ABS and have retrained to think "full brake pedal in a panic stop". Well, if you do this in a non ABS car, you could cause a dangerous wheel lockup.

It is scary, but we are getting to the point where all drivers need to think "what kind of computers does this car have... how should I drive it?"

Something to put this in perspective -
most modern jet aircraft are "fly by wire" where a computer actually controls the flight control surfaces, and the pilot just sends "suggestions" to the computer.

One of (many) benefits of this computer flight control is that the computer maintains 1g load on the passengers when doing banked turns. You take this for granted until one day when the pilot insists on switching to manual control mode and suddenly everyone feels like they are floating or squished in their seats as the plane turns.

It is a fact of modern life that you are putting your safety in the hands of some little computers when you get in a car, plane, etc.

Your computers are trying to keep you from crashing in your vehicle, but what do you do if the computers crash?!

 

[croddy]

TEG-you have a lot of information and some great suggestions. Wouldn't it be great if L-tunned offered a performance tunned ECU. I certainly hope they see some of your suggestions.

 

[niss mo]

Hi, experts and pros:
Do you know how to disable the automatic down-shifting in the M mode? If that is not possible, is there anything to change so that it will display the true gear after a down shift is done by itself.
Thank you very much.