Ls400 Trans 'slipping' When Cold

[goldtop]

So it's my first Winter with the Mk4 LS400. Couple of niggles, the most important of which is that if the temp is moderately low, the autobox seems to rev high and slip from a cold start.

Details:

0) cold start, say 3 degrees as indicated on the external temp display, where it might well have been about 0 degrees overnight

1) car starts on the button as normal in the morning

2) engage reverse to come out of parking space = okay

3) change to Drive = okay

4) but when I press the accelerator, the revs rise with very little motion

5) have to rev to 2500rpm (perhaps 3000rpm) just to get the car to move off at anything other than a snail's pace

6) the transmission seems to slip until the road speed catches up and then it does the same in the next gear

7) it's like this for about 2 minutes - it feels quite disconnected as it does

8) after that, it's works as normal, by which I mean that with gentle accelerator proddage in normal city traffic it changes up well before 2000rpm and with more of a direct throttle-to-road-speed feel

Thought I should ask here first, as it's not got that cold yet, and I should probably understand what's going on now rather than panic later. :)

I've had autos (Honda, Nissan, Mercedes and I can't recall any of them doing this).

[ambermarine]

The Lexus Ls400 does not respond to kick down until the engine is at normal running temprature so you will not get that kick in the back as you would when the car is warmed up.This was especially prelevant on the mark 1 which only had three forward gears and overdrive.

It may have something to do with the electronic throttle on the Mark 4 (the mark 1 was mechanical) with regards to the slow uptake and the gentler feel .

I have not noticed anything untoward on my Mark 4 .

Try to work between snow setting and normal drive and check if there is any noticable change before normal engine temprature is reached.

[ChrisIS200SportTTE]

Trans oil is cold, colder it is thicker it is. Try letting it warm up a little first. Sounds pretty normal to me. Sounds just like my IS300 until it warns up.

I honestly don't think there is too much to be concerned about. If when the car is at normal operating temperature everything is ok, then I'd say it's ok lol.

Now if it was struggling to select gear then you should be concerned.

Could always change the ATF

[goldtop]

Thanks guys. It's nothing to do with kickdown, and I'm not trying to get instant kick-in-the-back speed.

It happens from a standstill (first time in morning, and at each of the next 5-6 sets of traffic lights). If I use gently throttle, the car hardly moves - I need to rev up to about 3000rpm to get it move off at a normal pace (teh sort that I would at 1500rpm or so).

Trust me, after 4000m of problem-free driving with the LS400, this behaviour stands out like a sore thumb. It is definitely not usual, unrefined, and cannot be how the car worked when new. Buyers would have walked away! :D There are lots of other mentions online (all sorts of manufacturers), but I've never had a car that did it.

Not sure on the ATF point - some posts here say it's better not to mess with it!

[steve2006]

Is the fluid level corect when checked according to the owner's manual when hot and is it a nice cherry red colour with no burnt smell?

There is a temperature sender unit on these transmissions it may be worth checking that this is providing the correct output given the fault has only begun to occur since the ambient temperature has fallen.

I'm not convinced with the fluid flush method but I have had no problems when I did the 2 litres out/2 litres in method over a few days with 10 litres of new Type IV fluid.

[alien1974]

could it be a sticking solenoid?

[steve2006]

could it be a sticking solenoid?

I would have thought a sticking solenoid would prevent correct gear changes and selection, sounds more clutch/brake band related to me.

[steve2006]

It's transmssion morning sickness, generally happens when the fluid is cold and a bit thicker than when hot. My 1998 Mk4 does it on my upward sloped driveway in the cold weather. A quick workaround is to start the car, press the brake pedal and engage D for a few seconds, then back to N for a few seconds. Repeat this up to 3 times and you should find the transmission won't be slipping when you pull away.

Sent from my iPad using Lexus OC

Good idea, perhaps moving the selector from Park to Low and back slowly when cold started would help circulate the transmission fluid before moving off?

[cornershop]

On 08/12/2014 at 5:27 PM, goldtop said:

Thanks guys. It's nothing to do with kickdown, and I'm not trying to get instant kick-in-the-back speed.

It happens from a standstill (first time in morning, and at each of the next 5-6 sets of traffic lights). If I use gently throttle, the car hardly moves - I need to rev up to about 3000rpm to get it move off at a normal pace (teh sort that I would at 1500rpm or so).

Trust me, after 4000m of problem-free driving with the LS400, this behaviour stands out like a sore thumb. It is definitely not usual, unrefined, and cannot be how the car worked when new. Buyers would have walked away! :D There are lots of other mentions online (all sorts of manufacturers), but I've never had a car that did it.

Not sure on the ATF point - some posts here say it's better not to mess with it!

Goldtop - did you find a fix to this?  I've experienced something very similar earlier this evening in my 98 LS400.  I can't recall if it happened when the car was cold or warmed through.

[cornershop]

Just recalled, it happened near my house after a 45 min drive, so would have been at normal operating temps. 

I turned right at a traffic light, felt some hesitation, i.e. revs building but no movement, then suddenly it 'caught' and i shot off with a bit of wheel spin!

could this be throttle position sensor related? 

[goldtop]

Shirish, my LS400 only does it when cold (ambient under 8 degrees or so) and only until the temp guage has started to move. After that it's fine. And as one of the guys posted above, cycling from N to D and back a few times before driving off and at the first couple of traffic lights stops the problem from occuring. I presume that gets some trans fluid moving around inside the autobox.

But it cannot be normal behaviour as Lexus intended it. So for now, I treat it as an age-related issue that I can deal with. A transmission fluid service might cure it, but then that seems tricky to do fully/right.

[cornershop]

Thanks goldtop - similar symptoms then but not 100% the same. I wonder if mine is sensor related.

[steve2006]

On 24/01/2017 at 0:01 PM, cornershop said:

Thanks goldtop - similar symptoms then but not 100% the same. I wonder if mine is sensor related.

I doubt it as it sounds more mechanical than electrical, thinks to check are the fluid level and condition then the solenoid valves as these can become sticky in operation. Anything else and you would need an auto transmission specialist.

[cornershop]

Uh-oh, sounds expensive!

Will check fluid levels tomorrow 

Didn't happen at all today whilst driving.

[cornershop]

Post from 'Yamae' on the thread below suggests a throttle body clean may help matters:

http://us.lexusownersclub.com/forums/topic/73008-1998-ls400-shifting-issue/

[shanra]

My LS400 never slips like this and nor did my Soarer with the same gearbox, my Mercedes C220 has lumpy changes until it warms up but I've always been amazed at how smooth the box is on the LS now matter how cold. I'm amazed when told the fluid doesn't need changing yet it's on the service schedule and no fluid can last forever and must become contaminated. I've known many people have a fluid flush and filter change on their Soarers and be amazed at how much better it is afterwards. Take a look on the Soarer World forums and see what they think and ask Smiffie from the Soarer Sanctuary what he thinks about not changing the fluid on these boxes!

[shanra]

http://www.soarerworld.com/forum/showthread.php?31813-Soarer-auto-gearbox-faults-and-fixes

This may help

[cornershop]

Well I followed up on my initial research and started cleaning out the air mass mixer on the throttle body - bought some BG throttle body cleaner specifically.  This has definitely improved things however I'm thinking a throttle body clean will be required too.  

Fluid levels are fine and the oil still appears cherry red without smelling burnt.  I may get a second opinion on the transmission oil and take it to a specialist.

[JIM PIKE]

On 1/23/2017 at 11:21 PM, cornershop said:

Just recalled, it happened near my house after a 45 min drive, so would have been at normal operating temps. 

I turned right at a traffic light, felt some hesitation, i.e. revs building but no movement, then suddenly it 'caught' and i shot off with a bit of wheel spin!

could this be throttle position sensor related? 

Hi Shirish

Can you recall did you stop at the traffic lights or just slow down, then put your foot down again?.

Reason I ask is I have had my 400 for 3 years and it has done this since I bought it, not noticed at traffic lights but very noticeable when slowing and turning into a side road, put your foot down too hard and it kicks you in the back.

Looking sometime ago on the usa site many posts on it, basically its a trait of the gearbox on the early mk4,  gearbox confuses itself and can't decide which gear you need it to be in, but with your foot pressing harder the gearbox comes back to life with the 400 taking off rather rapid. I have learnt to just lightly touch the throttle when turning into side roads, almost too lightly sometimes.

Have read about cleaning the TB and so forth but the views on the usa site were mixed to say the least as too wether it worked or not. 

[JIM PIKE]

Hi Shirish

Forgot to add.

If you disconnect the Battery this trait does not appear strait away, I presume the gearbox needs to adapt to your driving again.

[cornershop]

Hi Brian - 

6 hours ago, JIM PIKE said:

Hi Shirish

Can you recall did you stop at the traffic lights or just slow down, then put your foot down again?.

Reason I ask is I have had my 400 for 3 years and it has done this since I bought it, not noticed at traffic lights but very noticeable when slowing and turning into a side road, put your foot down too hard and it kicks you in the back.

Looking sometime ago on the usa site many posts on it, basically its a trait of the gearbox on the early mk4,  gearbox confuses itself and can't decide which gear you need it to be in, but with your foot pressing harder the gearbox comes back to life with the 400 taking off rather rapid. I have learnt to just lightly touch the throttle when turning into side roads, almost too lightly sometimes.

Have read about cleaning the TB and so forth but the views on the usa site were mixed to say the least as too wether it worked or not. 

hi Brian

Its when i slow down and then speed up again, ie without actually stopping.  

See the thread here that 'Yamae' posted on - http://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/612441-still-low-idle-in-drive-at-stop-what-you-think.html#post8164859

As mentioned above, cleaning the air mix path has made a difference to part throttle response at low rpm (pickup is smoother), however the hesitation remains; I have noted that the revs increase, before drive kicks in and forward motion is resumed.

I'll get the t/b cleaned out - removal looks relatively straightforward, however i'm wary of disturbing the ageing electrical connectors and hoses.