LS400 1996 Poor idle/ engine cutting out

PeterF · April 13, 2017

I've got a problem with the idle on my 96 LS400, 145k miles. The car is up to date on its servicing and there are no warning lights on. The car starts fine, hot or cold, and drives normally without complaint under any driving conditions, except when the problem occurs. After a run of about an hour or more at motorway speeds, when the car is coming off the m-way and slowing down at the end of the slip road, engine revs will occaisonally drop so low that the engine cuts out. It will re-start from neutral without any problem and will not repeat this until it's on another long run. So, it won't cut out again when I stop at the next junction or set of lights. It only seems to be a problem slowing down after the m-way run. On a regualr trip I do, I've tried running with the cruise control off (normally it's on on m-ways) but this makes no difference, the problem remains.

I don't know if this is simply a problem with the idle speed adjustment - it ticks over at at about 400 RPM which I think is a little low - or somethink linked to idel air control or temp sensors.

Any pointers would be welcome.

ste42 · April 13, 2017

throttle body needs cleaning .you can put the air con on to keep the revs up to stop it stalling

steve2006 · April 13, 2017

There was a recall for this fault many years ago when the engine ECU was replaced with an updated version, take a look on clublexus for ECU capacitor problems and as Steve suggests try cleaning your TB.

Finally welcome to the LOC.

Malc · April 13, 2017

PeterF. I've given up trying to resolve this issue on mine ... it does exactly the same as you're experiencing . from time to time ........... had all the stuff done to overcome it but it persists and no-one anywhere has the answer ....... live with it I guess ............ I sometimes at the crucial moment use both brake and throttle at the same time and if I forget then I just pop it into neutral, coasting along, re-start the ignition and zap it into Drive and away we go again until the next time

Malc

Malc · April 13, 2017

4 minutes ago, steve2006 said:

There was a recall for this fault many years ago

Steve, I enquired of Lexus, a coupe of years ago, if I had any recalls outstanding ( the starter motor was one ) and I was assured there were none remaining extant.

And this cut-out issue remains for me ........... Cest le vie ......... seems to be a Mk3 hiccup, I never experienced it with my Mk1 or Mk2 and no-one has mentioned it with the Mk4

Malc

steve2006 · April 13, 2017

Hi Malcolm,

There was an upgraded ECU available although this will possibly not be the case today.

The original Engine ECU was 89661-50270, the upgrade was 89661-50271 and from what I remember this was to overcome the stalling issue.

Have you also checked the IACV for the sticky bearing problem?

Check out this thread from our USA club.

http://us.lexusownersclub.com/forums/topic/72023-95-ls400-ecu-upgrade/

Malc · April 14, 2017

blimey, thanks Steve, what a marathon read .. but so informative .............. I've advised my indy about the IACV and the Throttle Body and I'm sure he has done all that's possible there.

I used to be able to look at the revs vanishing to extremely low but of course i can't do that now. ( I said earlier that the rev counter has gone a bit haywirwe but doesn't affect the car's running at all )

What i did notice when it looked about to cut out at traffic lights ( after that long run on the Mway ) that had turned to red, that as i waited for them to go to green the revs just slightly edged up of their own accord and then there was no fear of stalling.

It doesn't seem to have been a Lexus Recall. The car drives brilliantly all the time and will doubtless continue to do so apart from this gremlin ............ that I'm managing to live with ok .................. anybody married here too ?

Life's full of little surprises and ups and downs, this issue just keeps me more alert and on my toes and stops me from falling asleep at the wheel after a long run in sublime comfort and opulence

I'll mention it again to my indy at the next service with the MOT .......... OMG it's due on 25th May

Malc

Spacewagon52 · April 14, 2017

17 hours ago, ste42 said:

throttle body needs cleaning .you can put the air con on to keep the revs up to stop it stalling

I had same problem on my old MK3. The air-con trick worked for me but it was a little disconcerting at the time. Sold the car before I managed to get the throttle body cleaned, told the new owner the problem.