Ls400 Revs Bounces At 1800 & 2000 Revs

[nereus4951]

i have a ls400 1992 and the revs idle spot on at 650 rpm but when i gently press the gas pedal slowly increase it to 1100 it is fine same at 1400 and 1600 but as soon it touches at 1800 & 2000 rpm the rev needle bounces down and up all the time but if i increase the revs to 2200 onwards it is fine it is always on 1800 & 2000 revs.please can some one give me an idea on how to sort this out, i have cleaned the throttle body and checked the vacumn pipes they are not cracked.

much appreciated

[Glenn007]

Hiya

Just a quick question, when the needle bounces around is it doing so in relation to the sound of the cars engine aswell? In other words can you hear the engine rev'ing eratically aswell as the needle? If not then it's probably just a signal problem to the rev counter or even a damaged spring in the dial needle.

Glenn

i have a ls400 1992 and the revs idle spot on at 650 rpm but when i gently press the gas pedal slowly increase it to 1100 it is fine same at 1400 and 1600 but as soon it touches at 1800 & 2000 rpm the rev needle bounces down and up all the time but if i increase the revs to 2200 onwards it is fine it is always on 1800 & 2000 revs.please can some one give me an idea on how to sort this out, i have cleaned the throttle body and checked the vacumn pipes they are not cracked.

much appreciated

[Glenn007]

Hiya

Just a quick question, when the needle bounces around is it doing so in relation to the sound of the cars engine aswell? In other words can you hear the engine rev'ing eratically aswell as the needle? If not then it's probably just a signal problem to the rev counter or even a damaged spring in the dial needle.

Glenn

i have a ls400 1992 and the revs idle spot on at 650 rpm but when i gently press the gas pedal slowly increase it to 1100 it is fine same at 1400 and 1600 but as soon it touches at 1800 & 2000 rpm the rev needle bounces down and up all the time but if i increase the revs to 2200 onwards it is fine it is always on 1800 & 2000 revs.please can some one give me an idea on how to sort this out, i have cleaned the throttle body and checked the vacumn pipes they are not cracked.

much appreciated

[nereus4951]

hi yes the engine revs erracticly as the needle bounces

[Glenn007]

Hi

You could try cleaning the injectors.... pouring some injector cleaner into the fuel tank. Another idea would be to get the timing checked.

Glenn

hi yes the engine revs erracticly as the needle bounces

[bazgtr]

When was your last time you changed the following?

Leads, Plugs, Rotor arms, Distubitor caps.

These simple changes will make a big difference on a LS400 its hard to believe. Most revs and any misses will be removed just by doing these simple service parts.

Get the parts from the US as miles cheaper. You're looking at around £120 - £150 for all itmes from the US and will be here in within seven days.

[steve2006]

It could also be the Throttle pot. giving erractic output due to dirty tracks/contacts especially as you have cleaned the TB some of the cleaner may have entered it and affected it electrically.

It operates in a similar way to the volume control on your hifi but instead of getting louder as you turn the knob it makes the car rev up more, if you have ever had a "noisy" volume control on your hifi/radio as you turn it up you will hear crackles and the volume level becomes erractic.

Since the problem you have is sensitive to the TP position ( the rev level) the same could be occuring here and substituting with a known good one would confirm this.

Looking at the throttle body it is the round plastic unit with the black connector coming out at the bottom.

If you click this link the 1st picture showns the TP with the wiring plug disconnected

http://www.lexls.com/tutorials/EFI/throttlebody.html

Hope you get it sorted.

Steve

[ssls400]

It could also be the Throttle pot. giving erractic output due to dirty tracks/contacts especially as you have cleaned the TB some of the cleaner may have entered it and affected it electrically.

It operates in a similar way to the volume control on your hifi but instead of getting louder as you turn the knob it makes the car rev up more, if you have ever had a "noisy" volume control on your hifi/radio as you turn it up you will hear crackles and the volume level becomes erractic.

Since the problem you have is sensitive to the TP position ( the rev level) the same could be occuring here and substituting with a known good one would confirm this.

Looking at the throttle body it is the round plastic unit with the black connector coming out at the bottom.

If you click this link the 1st picture showns the TP with the wiring plug disconnected

http://www.lexls.com/tutorials/EFI/throttlebody.html

Hope you get it sorted.

Steve

hi steve,i changes the tps of another lexus, not sure yet if it has helped but will test drive it first to see how it goes.the car was absolte spot on at one point then this silly thing started trying to put my finger on what it is.like you say it sounds like the tps.i did notice the screws that hold the tps was ever so slightly loose.could that contribute to it?when it touches at 600 revs at idle the car so of vibrates a bit but increase a little it stops say about 610rpm but thats only when i press the gas pedal.

any tipes on what i can do from here

thanks

simon

[Glenn007]

Hi

Just a note on the rev's. I also found that 650 rpm was the ideal setting on my LS400. Anything lower gave slight vibration.

Cheers

Glenn

It could also be the Throttle pot. giving erractic output due to dirty tracks/contacts especially as you have cleaned the TB some of the cleaner may have entered it and affected it electrically.

It operates in a similar way to the volume control on your hifi but instead of getting louder as you turn the knob it makes the car rev up more, if you have ever had a "noisy" volume control on your hifi/radio as you turn it up you will hear crackles and the volume level becomes erractic.

Since the problem you have is sensitive to the TP position ( the rev level) the same could be occuring here and substituting with a known good one would confirm this.

Looking at the throttle body it is the round plastic unit with the black connector coming out at the bottom.

If you click this link the 1st picture showns the TP with the wiring plug disconnected

http://www.lexls.com/tutorials/EFI/throttlebody.html

Hope you get it sorted.

Steve

hi steve,i changes the tps of another lexus, not sure yet if it has helped but will test drive it first to see how it goes.the car was absolte spot on at one point then this silly thing started trying to put my finger on what it is.like you say it sounds like the tps.i did notice the screws that hold the tps was ever so slightly loose.could that contribute to it?when it touches at 600 revs at idle the car so of vibrates a bit but increase a little it stops say about 610rpm but thats only when i press the gas pedal.

any tipes on what i can do from here

thanks

simon