95 Ls400 Stalls On Country Drives

[NickT]

Hi, I have a 95 LS400 and on country runs ( 100km or more) when i slow down to pull into a service station or stopping at traffic lights my car stalls. Its not consistent but can happen half a dozen times or more on one trip. Other Lexus sites have this thread and claim its a problem that affects the 95 and 96 LS 400 and is to do with a problem with the cars ECU.It seems to only happen on country driving ( never in city use) and only when the aircon is not on. Some of these sites claim that Lexus knows of the problem and it is related to a software problem within the ECU which controls the idle control valve. These sites claim that changing the valve will not solve the problem , you have to replace the ECU with the upgraded software .

Is anyone else having this problem?

NickT

[princkly]

I'm getting exactly the same problem. Did you find out what was causing this?

[grandpals400]

had same problem. for me it was a crack in the air intake after the air flow sensor (letting more air in than it thought). it was where the bendy section was - hard to see. runs much better now

[Steve]

this is quite common.. also car can start lurching when braking as the engine pulls forward and can open up the crack.

best have the engine mounts checked at the same time for wear and tear.

[gvm]

I'm having same problem as NickT, the first post in this thread. I spoke to the dealer today who said he was familiar with these symptoms and it is due to the cruise control motor overheating after long periods of highway driving. The engine stalls after slowing down from high speed cruising. Dealer reckons motor costs $1200 - $1400. Threads on other forums suggest problem might be with MAF (mass air flow?? thing) or as NickT says, the ECU. The car is due for a 120K km service so there is an outside chance a service might fix it. Any comments please? TIA... Greg

[NickT]

Hi Greg, I have had two idles valves replaced. The first one I had to pay for ( $900 ) and the problem remained . Lexus insisted it is a idle valve problem and not the ECU and replaced the idle valve at no cost to me. Guess what the problem remains . In the US lexus site , it is believed to be the fault of the ECU on the 95 and 96 LS 400 , but Lexus do not seem to want to know about it. Its all getting too hard and a replacement ECU is over $ 2000.The solution to the problem is easy though. if you have the air conditioning on the problem goes away.

[jay dee's gold]

I solved this problem in my 96 LS 400. Remove the air intake up to the second butterfly & clean any black deposits behind the second butterfly. My idle went from a worrying 300 to 400 RPM to a solid 650 RPM , it was a tip from my local mechanic. Lexus were no help they told me everything was perfect.

[OneDayWealth]

I am also having this problem. Car was built Feb 1996.

Research suggests that...

...be sure to know that these cars in their first 6 months of production have a faulty ECU (engine computer?).. mine had this and caused the car to stall when I would drastically slow my speed after highway drives of over 60 miles. before you buy a 96 ls 400, write down the VIN and call a dealer and ask them if that VIN has the old computer (part number ends in 302 or the new computer- part number ends in 303). if the service department has no clue what you're talking about, tell them to run a "tsb" on the 96 ls 400, specifically "low idle" and they will understand. they can then tell you if you have the bad computer or the good computer judging by the VIN...

I quoted a new ECU at about $2,600 (not sure if that's installed or inc GST or what)

I sure would like to learn it's not the ECU and that one of the above fixes would work (decarbonising the intake or a crack in the air intake after the air flow sensor for example) but I'm sure that Lexus will charge me a million dollars to do that as well. Problem is I trust no mechanics to know what they are doing these days and feel like whenever I go to one I am a lamb being lead to slaughter.

One clue is that if I shut the engine down and restart it it runs just fine and idles nicely. The front O2 sensors are new but the rear O2 sensors (at the cat) are original. I have 190k on the car so far. I bought it less than a month ago from Sydney and drove it back to Adelaide then drove from Adelaide to the Gold Coast and back over the last 2 weeks. It stalled in every town if I let it. Fortunately I am used to driving rough idling V8s and when I couldn't be bothered switching it off then on again every time I slowed for a town I just "two-footed" it to get me through. Very uncivilized.

If anyone has any suggestions... 041 505 2020

Thanks

Bill

[gvm]

Hi Bill, the quoted info is interesting. Did it come from one of the US forums?

I continues to have problems on my driving holiday this christmas. It did not happen everytime after a long 'high' speed cruise but I'm pretty sure the fault was independent of the airconditioner being on or off. It only happened after using cruise control, and would still happen even if I switched cruise control off prior to dropping speed down below 40kph.

Has anybody tried sourcing an ECU from the USA?

cheers

Greg

PS Is it true we can't get email notifications of updates to this thread?

[rastus]

hey there, i have friends with this similar problem and what it seems to be in both cases is an EFI relay overheating,one car is a 94 landcruiser and the other car is a sc 400 92 model. i have an ls 400 and havn't had any problems yet!!!.i dont know if this will be any help but you might want to give it a look.

good luck. :)

[gvm]

Research suggests that

...be sure to know that these cars in their first 6 months of production have a faulty ECU (engine computer?).. mine had this and caused the car to stall when I would drastically slow my speed after highway drives of over 60 miles. before you buy a 96 ls 400, write down the VIN and call a dealer and ask them if that VIN has the old computer (part number ends in 302 or the new computer- part number ends in 303). if the service department has no clue what you're talking about, tell them to run a "tsb" on the 96 ls 400, specifically "low idle" and they will understand. they can then tell you if you have the bad computer or the good computer judging by the VIN...

I have a 96 LS400 and I checked for the partnumber of my ECU but it doesn't end in 302 or 303. The writing on the outside of my ECU case is:

MPX Body

Toyota 89221-50031

123300-4070 12V

DENSO Made in Japan

TIA ... Greg

[gvm]

Hi Bill, the quoted info is interesting. Did it come from one of the US forums?

I continue to have problems on my driving holiday this christmas. It did not happen everytime after a long 'high' speed cruise but I'm pretty sure the fault was independent of the airconditioner being on or off. It only happened after using cruise control, and would still happen even if I switched cruise control off prior to dropping speed down below 40kph.

Has anybody tried sourcing an ECU from the USA?

cheers

Greg

PS Is it true we can't get email notifications of updates to this thread?

As reported in this forum, the car only ever stalled for me when cruise control was turned on but that has now changed. On this year's holiday, the car has started stalling after long periods of high speed driving even when cruise control was off. It is due for a service, but I wonder if that could explain the difference? TIA ... Greg

[310Art]

I also have a 96 LS400 and it too stalls on slowing down after running on the highway for over 30 mins. Any other suggestions than replacing a $2000 ECU? Has the dealer givin any support since the news of their cars surging and not stopping? I am in Los Angeles,

[gvm]

I also have a 96 LS400 and it too stalls on slowing down after running on the highway for over 30 mins. Any other suggestions than replacing a $2000 ECU? Has the dealer givin any support since the news of their cars surging and not stopping? I am in Los Angeles,

Hi 310Art. Sorry to hear of another LS400 owner with this problem. I haven't been involved with any of the interactions with Lexus about this problem but my understanding is they refuse to acknowledge a problem. This is serious because as you know, this sort of incident is a safety issue.

This thread lists many causes regarded as possibilities by forum posters

cheers

Greg

[Greavett]

Hi All,

This problem reminds me of a problem I had on a Corolla that came into the shop a few years ago. The symptoms were similar but not exactly the same. Vehicle was ok when cold and when driven softly, but as soon as you gave it a gut-full it died and coughed and spluttered.

Found eventually that the distributor oil seal had been leaking for some time. When the oil was cold (thick-viscosity) the car ran perfectly even when gunned. But once it had warmed up the oil was fluid enough to interupt the ignition spark and kill the car.

The reason i bring this to the table is that during town driving your vehicle may well be hot, but the start and stopping would probably not be enough to make the oil run to the rotor and cut the ignition. However, on long breaking, such as highway cruising and pulling off the slip way it could possibly give you the conditions needed to re-inact the Corolla syndrome.

It may be worth a look, seeing as the distributors....both of them run straight on the front of the cam sprocket, behind which sits the cam seals. Sounds like a tall tale, especially when you don't really see any oil leaking from around the cap area. But I can promise you, hot oil running in and around your distributor contacts definitely does not increase conductivity, it most positively decreases it to the point of ignition drop out.

Take your dissy cap off and have a quick look. You don't have to buy anything and it shouldn't take you long to remove it from your diagnostics!

Simon