Ls400 Running Rough

[stericker]

My 99 LS400 has started to run rough over the last few days, particularly on start up. When warm it gets better.

It is like it is not firing on all eight cylinders. Spark plugs ? I do not know when they were last changed. The car has

done 125,000 and most of my driving is in urban areas. Any thoughts gratefully received.

[steve2006]

Misfires will normally flag up a fault code and illuminate the Engine Malfunction Light on the dash, if you have an OBDII code reader check with this or have someone do it for you.

If you don't know the service history it could well be the plugs or a faulty coil pack or indeed many other things.

[ManicMark]

plugs every 60k so at 125 they are due. try wd40 on the electrics & unplugging & plugin in the coil connections first.

[stericker]

Many thanks Steve and Mark. Nothing has come up on the dash. Probably is plugs and/or coils. Will get it checked out.

[ipwn]

I'd put money on an air leak or something like that.

[stericker]

The LS400 ('99) had a full service and new spark plugs yesterday at JEM who are a large Japanese vehicle garage

in North London. It is still running rough. They say it is either ignition coil(s) or fuel injectors.If it is coils where is the best place

to source them at a reasonable price ? And is it likely to be more tha one coil ? Is there an easy way to test them ?

I notice that it is taking a lot longer to reach running temerature in the morning - any clue here ?

Any suggestions gratefully received. Incidently nothing is showing up on the dash. They plugged in an analysis thingy and

all that came up was a faulty (?) oxygen sensor.

[brendangeorge]

The LS400 ('99) had a full service and new spark plugs yesterday at JEM who are a large Japanese vehicle garage

in North London. It is still running rough. They say it is either ignition coil(s) or fuel injectors.If it is coils where is the best place

to source them at a reasonable price ? And is it likely to be more tha one coil ? Is there an easy way to test them ?

I notice that it is taking a lot longer to reach running temerature in the morning - any clue here ?

Any suggestions gratefully received. Incidently nothing is showing up on the dash. They plugged in an analysis thingy and

all that came up was a faulty (?) oxygen sensor.

Hi

If their OBD reader indicated a fault you should have the engine management light on the dashboard on. The fault could be cleared by disconnecting the Battery or with a reader but if intermittent will come back - if permanent will not clear for long. If you had the car serviced and plugs changed I am a little surprised that they could not give you a better diagnosis than it could be coils or injectors. Don't fall in to the coils trap my LPG installer did and it cost (his insurance) a packet - when there was an air leak in the plenum (as suggested by Sam) which caused the car to go into limp home mode (miss some of the cylinders) because it was running too lean. If one of the oxygen sensors is faulty you should see the management light come on - check it comes on when you turn the ignition on because the light could be faulty :).

You may see a faulty Lambda sensor because of something else - you need a mechanic and test kit not just test kit.

I have a 430 but the engine etc is basically the same as the 400 and had a very small (pin hole) in the exhaust that kept indicating a faulty lambda sensor - a welder fixed that. You need somebody, who has the correct kit - my OBDII reader cost £10 - my garage uses one that cast £2K - and who knows what they are doing. Swapping bits will not work if as Sam suggests you have an air leak.

You mentioned it gets better when warm - my air leak got worse when warm but that may not mean anything.

Good luck

Bren

[steve2006]

I wonder if the clue here is that the engine performance improves as the engine warms up?

It would be wise to check out the engine coolant temperature sensor, if this has gone off on one it could be telling the ECU the engine is cold and therefore overfueling when it is in fact warm and the fuel trim should be adjusted leaner. This problem will cause rough running/misfire effect and possibly why a faulty 02 sensor flagged up if the fueling is seen as out of range of the sensor.

Just make sure the engine management light comes on with the ignition on then goes off a few seconds after starting.

If it were to be an air leak wouldn't this be present at all engine temperatures?

Still worth checking as suggested the electrical connection plugs to each coil pack a bad connection in one of these could fully make as the engine warms up.

[plexus914]

I've read a lot about bad LS400 ECUs.

Please, read this carefully:

http://www.clublexus.com/forums/ls400/656360-all-my-crazy-lexus-issues-solved-ecu-leaking-capacitor.html

[stericker]

Further to the 'running rough' problem. Am a happy bunny today as the problem has been sorted by

my little independent local garage. He suspected coil(s) as the spark plugs had been renewed. By process

of elimination he found that it was not coil(s) but that the O/S rear fuel injector was not injecting. It

transpires that the front 'pots' have a different fuel injector to the rear 'pots' For some reason he had

to send to Germany for the part - (he did not want to fit a second hand one)- £146 plus VAT- but it came within three days.

Total for the job £295 (inc. VAT) which I thought was pretty good.

Is it unusual to have a fuel injector problem on an LS400 ? And what might have caused it ?