1999 LS 400 - on pulling away there is a delay in engaging gear and car lurches forward

Stanwithaplan · November 5, 2022

Hi All,

I am after some advice please? The Golden Goddess has started to have what feels like a slight delay when pulling away and lurches forward with sudden gusto. It seems particularly noticeable after negotiating speed bumps, now I can mitigate this by treating the accelerator as being more fragile than a butterfly's spectacles but its' spoiling the wafting experience?

The transmission fluid was changed about 11 months/16K miles ago, so I'm thinking it shouldn't be that??

Any pointers would be appreciated please.

Malc1 · November 5, 2022

no idea, sorry !

Malc

Supafly · November 7, 2022

When I first bought mine it had a similar (not as severe though) issue. After some research I found that the throttle cable and some throttle body air holes could be culprits.

My throttle cable did require some small adjustment and I took the cover off the throttle body and cleaned out the holes and throttle body/butterfly. This did the trick for me and I've not had the issue again in over four years.

Supafly · November 7, 2022

This thread has images of what I'm referring to...

1998 1999 2000 ls400 throttle body air mix path cover plate - ClubLexus - Lexus Forum Discussion

Supafly · November 7, 2022

The throttle cable adjustment was very easy too... from memory you need to release the lock nut and then adjust so that there is no slack on the cable with the throttle in its resting position.

When adjusting make sure to not go too far and cause the butterfly to open a little.

Razor61 · November 13, 2022

On 11/7/2022 at 4:18 PM, Supafly said:

This thread has images of what I'm referring to...

1998 1999 2000 ls400 throttle body air mix path cover plate - ClubLexus - Lexus Forum Discussion

That’s a very interesting post and link thanks, my car does seem to accelerate and take off quicker than normal/expected sometimes - mainly when pulling away quickly and put your foot down to get out of a junction quick for example. It’s a bit like the throttle cable is sticking slightly and then suddenly off you go. I’ll have a look at this and clean the air mix path holes described, can’t do any harm. The gasket for the cover plate isn’t available anymore but it’s easy to buy a sheet of gasket material and make one. Making a new thicker cover plate with a domed cavity makes sense as well, I’ll look into getting one made.

Malc1 · November 13, 2022

4 hours ago, Razor61 said:

my car does seem to accelerate and take off quicker than normal/expected sometimes

does she just need a significant good " blow out " at some sort of excessive speed and acceleration mode ? For a jolly good long challenging run

worked wonders some years back when i had my used car sales business ...... remembering a BMW 318i and a huge Volvo estate that hadn't been " driven fully " over their lives .... they then performed miraculously better thenceforth for me . not so hot on speed limit adherence in those days tho'

Malc

Razor61 · November 14, 2022

21 hours ago, Malc1 said:

does she just need a significant good " blow out " at some sort of excessive speed and acceleration mode ?

I don't think so, done some proper testing and there isn't an issue with the car taking off quicker or delayed, it just 'seemed' like it was.
I'll still have a look at the air mix path holes and clean them though.

Supafly · November 14, 2022

You're very welcome.

The 'Italian service' is a favorite of mine and one I regularly do 🙂

In this instance the carbon builds up over time and requires a manual clean. I was able to reuse the gasket and was surprised at how easy the screws were to remove.

I do still experience the odd hesitation now and then too Paul, as you described. I think this is down to the design and technology which is exacerbated when you press the throttle a little slowly at first then floor it. When I'm at a junction like that (and sometimes when the conditions are a little slippery) I turn off the VSC and sometimes put it into L too, as that gives me more control.

The traction control is wonderful in these and sometimes so subtle that you don't even notice it. I've found that a little slip will cause it to pull a significant amount of power when at junctions, which feels like it's a dead spot/lull in performance but is actually the system working as intended. Which is why I'll turn it off in certain situations/road conditions.

Supafly · November 14, 2022

In a nutshell... The cleaning and cable adjustment solved 95% of my issue and what's left, I believe, is the car behaving as it was designed to.

Stanwithaplan · November 15, 2022

Thankyou very much Supafly, your advice is logical much appreciated. I will definitely do as you advise and feedback.

Stanwithaplan · January 25, 2023

Quick update, I got the throttle cable adjusted and throttle body cleaned. In doing so, we found a hole in the pipe coming from the air intake, it looked like someone had tried to block the hole previously and it blew out. So it took a day of going around Sharjah scrapyards to find a replacement (because my car is an American import and that apparently is different to the normal ones normally found in the Middle East -who would have thought???). Problem solved, car now accelerating very smoothly and as a bonus the Engine Management light has been out for over a week now, which is great (cos I thought that was either faulty o2 sensors or the cat).

Malc1 · January 26, 2023

c'mon Stan , you know by now from all the posts on this Forum that the Ls400 is more or less invincible and with a little astute maintenance could last forever

Malc

Supafly · January 26, 2023

17 hours ago, Stanwithaplan said:

Quick update, I got the throttle cable adjusted and throttle body cleaned. In doing so, we found a hole in the pipe coming from the air intake, it looked like someone had tried to block the hole previously and it blew out. So it took a day of going around Sharjah scrapyards to find a replacement (because my car is an American import and that apparently is different to the normal ones normally found in the Middle East -who would have thought???). Problem solved, car now accelerating very smoothly and as a bonus the Engine Management light has been out for over a week now, which is great (cos I thought that was either faulty o2 sensors or the cat).

Glad to hear that you got it sorted. Thank you for following up, never know who it could help in the future 🙂

So unmetered air was the cause of your issue, which reminds me... I remember reading somewhere about the injector seals failing and causing similar issues. A way to check for this or other leaks is to spray carb/brake cleaner or propane/butane from a blowtorch around the intake paths to see if it affects the running of the engine... HUGE WARNING this is using flammable fuel to check for leaks, so please only attempt if you know what you are doing and what the risks and precautions are.

For the more professional, there are smoke machines and leak detectors to accomplish the same but without the fire hazard 🙂 (albeit with more cost).