Engine Stalling After A Run

[BigMartin]

As mentioned in my Introduction thread, my 1996 Series 3 LS400 has started stalling randomly. It’s got 163K on the clock.

It usually stalls when slowing down from a high speed run, so mostly on Motorway Slip Roads or A Road roundabouts. Whether the exit has uphill or downhill Ramps make no difference as it has stalled on both. Usually all the dashboard lights begin to flicker before it actually stalls, though it normally keeps running until I am down to around 2mph or less. Sometimes it does cut-out at higher speed, usually if I am really breaking hard. I’ve just had a cut-out at around 20mph while going round a bend at the end of a dual carriageway slip road. Every time it happens, it restarts immediately, with normal tickover.

If the car doesn’t stall outright, then the Tickover gets progressively lower. I’m getting good at coasting to a stop with a tiny bit of throttle to just keep it alive. It doesn’t make any difference if put in a lower gear. If it stops without stalling then I can put it in neutral and use accelerator to give 1000rpm and keep it running. Same again, when it does finally stall, restarts immediately, with normal tickover.

If you press the aircon button, the tickover rises to compensate for the extra engine load, so it doesn’t usually stall. Hard braking on motorway sliproads can still stall the engine with the aircon on.

This doesn’t seem to be weather dependent (Hot/Cold, Wet/Dry)

Once the tickover starts to fall, it doesn’t recover back to normal until the engine is restarted. I could stop at several consecutive junctions with low tickover and the engine almost laboring, but the tickover only ever recovers when the engine is restarted.

If I just drive it around town, like I have today, then no problems, the tickover stays normal. It needs to have some kind of sustained 5 minute run at speed.

Any ideas? I don’t want to go to a garage with this problem as the car isn’t worth too much now and it’s going to be uneconomic to have it looked into on huge detail.

[Malc]

Hey, I have a very similar issue with mine too ..... when I'm motoring and the fault happens, I just zap it into neutral and then re-start the ignition ..... at whatever speed, it seems to work ok then .......... until the next time.

No rhyme nor reason to it and sometimes it is just absolutely fine....... with no issue for weeks/months on end

I have, just yesterday emailed my indie mechanic chap for an explanation and for him to ponder the big Q.

When I get a response I will let you know.

He has been aware of this issue for ages but didn't have a clue !!! He initially cleaned out the throttle body but that hasn't seemed to resolve

I have thought maybe it's an Oxygen sensor.

Malc

[BigMartin]

Thanks Malc, please let me know what your independent says and I will ask one here too. Let's see if we get the same reply.

[petayV8]

Sounds like a faulty sensor

[Rotty]

I dont know if this post on the american forum is helpful to you..

http://us.lexusownersclub.com/forums/topic/30723-step-by-step-instructions-for-iacvidle-air-control-valveiscthrottl/

you need to sign up to see the photos etc..

Alan

[Malc]

Thanks for the USA post ......... I've referred it to my chap.

Malc

[BigMartin]

Malc - Any news/views from your mechanic?

I spoke to my Independent on Friday (He used to be a workshop foreman in a main dealer)

He immediately suggested the next thing to do is clean out the throttle bodies, without me having to suggest anything based on the advice I was getting elsewhere. He says it will be about an hour to do at £55/Hour. It's booked in for Friday 17th.

As to why the tickover recovers when you restart the engine (when if throttle bodies are not closing properly you would think they don't close properly after a restart either) - his comment was that everything goes into a default condition and after a few minutes the ECU starts to correct back to optimum again, meaning the not fully closed throttle bodies then start to cause problems again.

I will report back here on whether this fixes anything.

[PEPE]

Yes I bet it is a dirty throttle body. I look forward to Martin's report.

[Malc]

I haven't yet heard back from my chap. I'll call him over the next day or two.

I doubt the throttle body is the issue in my instance though. He cleaned it out ok last year, it needed it, BUT that didn't resolve the problem !

Malc

[Malc]

Update from me: phoned my guy yesterday and he has been so incredibly busy since b4 Xmas that he hasn't yet had the time to think about it ............ he will, it's just time !

Malc

[steve2006]

There was apparently a problem with the engine ECU causing this exact problem and there was a recall for a modified version to be fitted.

I would have thought that all of them had been done at the time but maybe there are a few that missed it.

Another possible cause could be the IACV which do tend to get gummed up and sticky,it may be that it fails to open quickly enough after a long run being closed to provide the correct idle speed airflow.

Like the TB this can also be cleaned.

[BigMartin]

Thanks Steve2006.

I just collected my car after the Throttle Bodies were cleaned out. They assured me they were "gummed up quite badly" and that the tickover is definitely a little higher than it was before. I need to take the car for a run now and see how it performs as the stalling never really happened around town and only after a higher speed run.

Here's hoping and I will report back once I know one way or the other.

[PEPE]

I am waiting with bated breath for your feedback, Martin, as I've always thought a dirty TB was the problem.

[Malc]

what's the IACV please ?

Malc

[steve2006]

what's the IACV please ?

Malc

Idle Air Control Valve, when the throttle plate is fully closed i.e. the engine is at idle speed this valve opens to supply bleed air into the intake manifold to maintain idle.Without this the engine would receive very little air and stall.

It is the cylindrical device with several hoses coming off it mounted on the front of the plenum chamber ( the bit with the lexus logo on it)

Not the best quality video but shows what's what.

[Malc]

Thank you Steve, I'll get my guy to look at this.

Malc

[Dale_V]

Its the ECU at fault as has been stated. My 96 had the exact same issues of stalling after a run, then slowing down such as on a slip road. I replaced the ecu with the revised one from a 1997 and the problem has never come back, its been over a year now.

[Malc]

Dale hi, thanks for that. I doubt it is the ECU though ......... when I bought my car off ACLex the LOC Parts guy at Lexus Poole, the car had FULL Lexus service history ................. I doubt very much that it would have missed the re-call.

If the ICAV cleaning doesn't solve the issue then I'm hoping my guy will figure out the solution ( somehow ) :luck:

Thanks

Malc

[BigMartin]

Thanks Dale,

Is there any way I can tell whether my ECU has been swapped out or not?

What did the replacement cost you?

I might find when I drive it out of the town later today that the problem has been fixed anyway.

Regards,

Martin

[Malc]

Fingers XD for you

Malc

[Dale_V]

The replacement was from another ls400 I bought to get some spares off.

I got the info regarding the ecu issues from the USA forums, there is a revised part number for the updated ecu, cant remember what it is off the top of my head.

Malc, the 1uzfe is a clean running engine, its unlikely to be a dirty ICV at fault, it will be the ecu

[BigMartin]

Well, took it out up and down a dual carriage way tonight, randomly pulling off at junctions and slowing down as quick as I can. In one case I braked from 60mph to a stop in 4 seconds or so.

The car does not stall and the tickover seems to stay over 600rpm all the time.

I'm hoping this is fixed.

The real test will be the proper trips to and from work next week - 5 days is 450 miles. I will report back then, but it looks good at the moment.

I will be very happy if it stays that way.

[BigMartin]

Well I have been backwards and forwards to work for a week, clocking up 500 miles on motorways and A Roads. Lots of high speed burst with stops for roundabouts and junctions.

This car will not stall, will not go to a low tickover and won't give me any indication that it is going to.

For me, the Throttle Body clean has resolved all the problems I reported in the first post.

Thanks to those who shared advice, both this post and on PM and Good Luck to the other people reporting the same thing.

I'm happy.

[Malc]

Good result for you .......................

Malc

[ste42]

had similar issues a few yrs ago with mine again it was throttle body but used to switch air con on when I was about to slow down to keep the revs a little higher