1995 LS400 needs too much brake force to keep stopped at traffic light
10-14-23, 05:27 PM
#1
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1995 LS400 needs too much brake force to keep stopped at traffic light
Hi, My LS idles at correct idle speed, approx 600+ rpms, but when stopped at a traffic light, it always feels like I have to apply too much pressure to keep the vehicle from creeping forward. In fact, just barely letting of the brakes will let it move forward. The front brakes where done 10,000 miles ago, rears were just replaced. Braking while the car is in motion from high or low speed is excellent and I don't feel like I have to use excessive force to bring the car to a stop. The only other thing I've noticed is, if you let the car coast without your foot on the gas or brake, the car will drive at up to 10 mph or more by itself.
I've tried for hours searching and I keep getting either unintended acceloration info, or car dying while breaking. Mine doesn't do any of that. My revs aren't abnormal, nor do they increase/ decrease by themselves (other than the normal cold start revs). I read somewhere that it's a Lexus thing, but that was referring to the GX 4WD. I also keep seeing stuff about the master cylinder, but that doesn't explain why the car will drive itself without boosted rpms. On a flat road (we have zero hills or inclines), I brake the car down to 35 mph, I let my foot off the gas and let the car coast at 35mph for what seems like an eternity. No acceleration and rpms were at idle speed. Is this normal? I've had cars accelerate by themselves due to stuck throttles, but this is different.
I've tried for hours searching and I keep getting either unintended acceloration info, or car dying while breaking. Mine doesn't do any of that. My revs aren't abnormal, nor do they increase/ decrease by themselves (other than the normal cold start revs). I read somewhere that it's a Lexus thing, but that was referring to the GX 4WD. I also keep seeing stuff about the master cylinder, but that doesn't explain why the car will drive itself without boosted rpms. On a flat road (we have zero hills or inclines), I brake the car down to 35 mph, I let my foot off the gas and let the car coast at 35mph for what seems like an eternity. No acceleration and rpms were at idle speed. Is this normal? I've had cars accelerate by themselves due to stuck throttles, but this is different.
10-14-23, 06:41 PM
#2
The brakes are quite soft so you need a fair bit of pedal travel. This is just how older cars are. Modern cars (and some older ones like Porsche) do tune their brake pedals to have far more pressure at the "top" of the pedal. But in our 400's, yeah you need to retain a fair bit of pressure on the brakes to hold the car vs. the torque converter.
The idle speed sounds about right too. 600 revs is right, and yeah if you just let it coast it'll go quite quickly.
At least, this is how my car also drives. I drive a lot of different cars and getting back into mine it doesn't feel terribly abnormal to me, and I'm quite sensitive to these things.
Will it actually retain 35mph? Or will it slowly drift down. The coast ability of this car I would characterize as "higher than normal".
Did the car drive like this before the brakes were done?
The idle speed sounds about right too. 600 revs is right, and yeah if you just let it coast it'll go quite quickly.
At least, this is how my car also drives. I drive a lot of different cars and getting back into mine it doesn't feel terribly abnormal to me, and I'm quite sensitive to these things.
I brake the car down to 35 mph, I let my foot off the gas and let the car coast at 35mph for what seems like an eternity.
The front brakes where done 10,000 miles ago, rears were just replaced.
Did the car drive like this before the brakes were done?
Last edited by 400fanboy; 10-14-23 at 06:45 PM.
10-14-23, 08:29 PM
#3
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It will eventually slow from the 35 mph but it will continue at 10 mph.
Rear brake replacement made no difference. (And didn't take away the "tiss....tiss.....tiss..." noise that comes from the rear wheels at slow speeds either.)
The accelorator pedal is hard to push, so much so, that when I get in my Jeep Grand Cherokee, I'm taking off like a bandit. That made me think it could be throttle position sensor, but that wouldn't explain no increased revs during coasting. From what you said, I'm thinking it's just the way it is, which makes me feel better. I can live with it. I would even go as far as to say the long coasts seem like it would be a very "Lexus" like thing. The high pressure to hold it at stand still and hard to press accelerator do not.
Overall, I guess I shouldn't complain for a car that's 28 years old. No one that rides with me can get over how such an old car can ride with zero squeaks or rattles.
Rear brake replacement made no difference. (And didn't take away the "tiss....tiss.....tiss..." noise that comes from the rear wheels at slow speeds either.)
The accelorator pedal is hard to push, so much so, that when I get in my Jeep Grand Cherokee, I'm taking off like a bandit. That made me think it could be throttle position sensor, but that wouldn't explain no increased revs during coasting. From what you said, I'm thinking it's just the way it is, which makes me feel better. I can live with it. I would even go as far as to say the long coasts seem like it would be a very "Lexus" like thing. The high pressure to hold it at stand still and hard to press accelerator do not.
Overall, I guess I shouldn't complain for a car that's 28 years old. No one that rides with me can get over how such an old car can ride with zero squeaks or rattles.
10-14-23, 09:21 PM
#4
What condition is your throttle body in? The butterfly valve & associated area.
Here's how you take a look at your TPS. But I think this seems unlikely, you weren't really describing normal TPS issues.
https://www.lexls.com/tutorials/EFI/tps.html
What year is your Jeep? Modern cars have significantly more sensitive throttles, especially in the first 1\4 inch of pedal travel.
But beyond this I honestly can't really say what is\isn't normal with your car. All cars with a torque converter will idle, with no brakes, at 5 or 10mph depending on a bunch of factors.
Here's how you take a look at your TPS. But I think this seems unlikely, you weren't really describing normal TPS issues.
https://www.lexls.com/tutorials/EFI/tps.html
What year is your Jeep? Modern cars have significantly more sensitive throttles, especially in the first 1\4 inch of pedal travel.
But beyond this I honestly can't really say what is\isn't normal with your car. All cars with a torque converter will idle, with no brakes, at 5 or 10mph depending on a bunch of factors.
Last edited by 400fanboy; 10-14-23 at 09:25 PM.
10-14-23, 09:50 PM
#5
So the RPM is 600+ in drive at a stop light. Now put the transmission in neutral - what are the RPM's now? Report back the number.
10-14-23, 10:09 PM
#6
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Thread Starter
What condition is your throttle body in? The butterfly valve & associated area.
Here's how you take a look at your TPS. But I think this seems unlikely, you weren't really describing normal TPS issues.
https://www.lexls.com/tutorials/EFI/tps.html
What year is your Jeep? Modern cars have significantly more sensitive throttles, especially in the first 1\4 inch of pedal travel.
But beyond this I honestly can't really say what is\isn't normal with your car. All cars with a torque converter will idle, with no brakes, at 5 or 10mph depending on a bunch of factors.
Here's how you take a look at your TPS. But I think this seems unlikely, you weren't really describing normal TPS issues.
https://www.lexls.com/tutorials/EFI/tps.html
What year is your Jeep? Modern cars have significantly more sensitive throttles, especially in the first 1\4 inch of pedal travel.
But beyond this I honestly can't really say what is\isn't normal with your car. All cars with a torque converter will idle, with no brakes, at 5 or 10mph depending on a bunch of factors.
The Jeep is a 2015 V6 and is drive-by-wire. Definitely much more responsive off the line and quicker to downshift, but the Lexus will spank it on the highway during 70 mph downshifts even though the Jeep has twice as many gears to choose from. I can only imagine what 30+ extra horsepower and an extra gear do for VVT versions of the LS400.
10-14-23, 10:48 PM
#7
Moderator
Have you checked the brake booster and the hose to it?
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10-14-23, 11:29 PM
#8
We're off the topic here of your braking force. I can't say forsure what would cause the engine to generate more power at what should be idle. If you're idling at 600rpm in neutral, then I think this is just your personal expectations of how the car drives relative to everything else you've ever driven. Have you driven other older cars? What else other than the Jeep. If you've only been in modern stuff, the pedal inputs and calibration of the LS400 is quite different.
Did they replace the spark tube seals? You didn't mention those... and you have to remove the valve covers to replace them when they start leaking oil, and they're like $2 each so there's no reason not to do it while you've got the covers off.
Not an awful idea to do, the part is like 20 bucks and easy to do. I think it's unlikely to cause your current concerns, if they are concerns, but it's good preventative maintenance. However, I wouldn't mess with the wire connectors until they break.
Well the Lexus can respond just as quickly off the line, you just need to give it more throttle input with your foot. The acceleration isnt' what I'm talking about, it's how senseitive the throttle is. And as I suspected, modern fly by wire Jeep (and most modern economy cars) is very sensitive compared to old Lexus, all BMW's and some Porsches.
Yes the VVT adds a lot of power in the midrange. The peak power gains are 30 horserpower, but I think it gains something like 50lb\ft at 3000rpm. The area under the curve gains are massive and that's where it really makes a difference.
Anyway, since I'm in there, I'll also be replacing both the temp sensor and sender. My temp gauge reads OK, but the sender has too much visible corrosion and I'm not happy with how the wire was rigged (Which is weird because every record has this car being serviced by Lexus throughout its entire life). I know it's only a matter of time before it starts having issues, so I figured I'd do both. I'll also be replacing one of the fuel injector's wire connector because the clip that holds it in place is broken and it gets loose which I know is not good.
The Jeep is a 2015 V6 and is drive-by-wire. Definitely much more responsive off the line and quicker to downshift, but the Lexus will spank it on the highway during 70 mph downshifts even though the Jeep has twice as many gears to choose from. I can only imagine what 30+ extra horsepower and an extra gear do for VVT versions of the LS400.
Yes the VVT adds a lot of power in the midrange. The peak power gains are 30 horserpower, but I think it gains something like 50lb\ft at 3000rpm. The area under the curve gains are massive and that's where it really makes a difference.
10-15-23, 11:19 AM
#9
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10-15-23, 11:30 AM
#10
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We're off the topic here of your braking force. I can't say forsure what would cause the engine to generate more power at what should be idle. If you're idling at 600rpm in neutral, then I think this is just your personal expectations of how the car drives relative to everything else you've ever driven. Have you driven other older cars? What else other than the Jeep. If you've only been in modern stuff, the pedal inputs and calibration of the LS400 is quite different.
Did they replace the spark tube seals? You didn't mention those... and you have to remove the valve covers to replace them when they start leaking oil, and they're like $2 each so there's no reason not to do it while you've got the covers off.
Did they replace the spark tube seals? You didn't mention those... and you have to remove the valve covers to replace them when they start leaking oil, and they're like $2 each so there's no reason not to do it while you've got the covers off.
I told them about the tube seals (and they charged me for them) after reading the posts on the forum. As far as I can tell, no old or new leaks.
10-15-23, 02:24 PM
#11
How far down do you have to press the pedal down to hold the car at a stop?
Also, what is the condition of your brake fluid and when was it last changed? Is the fluid black? - if it's really dark, then it could be holding in moisture and that should be changed.
Definitely agreed with Yamae - check the booster and the hose first. It could be a vacuum leak.
Also, what is the condition of your brake fluid and when was it last changed? Is the fluid black? - if it's really dark, then it could be holding in moisture and that should be changed.
Definitely agreed with Yamae - check the booster and the hose first. It could be a vacuum leak.
10-15-23, 04:57 PM
#12
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How far down do you have to press the pedal down to hold the car at a stop?
Also, what is the condition of your brake fluid and when was it last changed? Is the fluid black? - if it's really dark, then it could be holding in moisture and that should be changed.
Definitely agreed with Yamae - check the booster and the hose first. It could be a vacuum leak.
Also, what is the condition of your brake fluid and when was it last changed? Is the fluid black? - if it's really dark, then it could be holding in moisture and that should be changed.
Definitely agreed with Yamae - check the booster and the hose first. It could be a vacuum leak.
10-15-23, 05:45 PM
#13
Halfway down the pedal is a ton. You're right that is excessive. I should have asked that question.
Brake fluid should be clear with a very light yellow tint.
Green says moisture is in the system. You may have internal brake system corrosion\damage if it's been like this for a while (it probably has), and you almost certainly have air\water in the brake system which can certainly cause a spongy feel to the brakes.
You need to clear the entire system ASAP.
Brake fluid should be clear with a very light yellow tint.
Green says moisture is in the system. You may have internal brake system corrosion\damage if it's been like this for a while (it probably has), and you almost certainly have air\water in the brake system which can certainly cause a spongy feel to the brakes.
You need to clear the entire system ASAP.
Last edited by 400fanboy; 10-15-23 at 10:00 PM.
10-15-23, 09:39 PM
#14
Agreed with 400fanboy. It's time to change your brake fluid. That could also be affecting your brake feel
Having the pedal about halfway down sounds normal. After changing the brake fluid and flushing out the old stuff, I would check to see how things feel again. Keep an eye on your new fluid to make sure it doesn't turn dark too quickly. It should stay pretty clear and yellow for the first few months at least (more or less).
Having the pedal about halfway down sounds normal. After changing the brake fluid and flushing out the old stuff, I would check to see how things feel again. Keep an eye on your new fluid to make sure it doesn't turn dark too quickly. It should stay pretty clear and yellow for the first few months at least (more or less).
10-16-23, 07:46 AM
#15
Check the vacuum lines to your brake booster for cracks or leaks. If its leaking from the diaphragm inside the booster you'll have to replace the whole brake booster assembly.
Mine went out at around 280k. Replaced with one from O'Reillys in a pinch, but that went out a few months after. They replaced it under warranty but I had to go through the hassle of reinstalling it. I would go oem if you can, if not maybe try NAPA.
Mine went out at around 280k. Replaced with one from O'Reillys in a pinch, but that went out a few months after. They replaced it under warranty but I had to go through the hassle of reinstalling it. I would go oem if you can, if not maybe try NAPA.