Check Engine !

[stericker]

I use my Mk 4 everyday and it has been running smoothly. Yesterday as I was nearing work I was caught in

traffic and at idle the engine became rough. After acceleration it felt smooth but the 'check engine' flashed up.

Continued to work (only 5 minutes). After work engine started fine and no 'check engine' came up all the way home.

Today the 'check engine' came on at almost the same point in the journey to work. Any thoughts ?

 

[cornershop]

I’m no expert but I’d start checking the Battery at idle, make sure the alternator is charging.  A duff Battery can generate lots of issue.

[Cotswold Pete]

I assume the ECU is generating some codes that you could get checked out by garage with right kit.

Rough engine at idle could be a number of things, and getting Battery checked out is usually quick (and free), but having run with failing batteries a few times, I found they upset the alarm but never had Engine Check light come on even with Battery in death throes and a 200 mile journey ahead of me.

Might be worth looking at cleaning throttle body, though had two cases where as dirty as you like, LS stalling and up and down like a Yo-Yo at idle, but never have engine light come on.

Best of luck getting it sorted.

[steve2006]

First job is to have the codes read, even if the light is off when checked the code should be stored in the ECU memory, guessing the cause is the most time consuming and expensive method.

[stericker]

Many thanks Shirish, Pete and Steve for your suggestions. I shall go to my indie to have the codes read.

I seems like a 'heat' thing as yesterday my drive home took longer than usual and 'check engine' came up

a few yards from home. The coolant level is correct and there are no other warnings on the dash board.

The Battery is only a few weeks old.

[Cotswold Pete]

Maybe check engine oil, most likely not related to problem, but once had a Renault where engine light came on even though oil light did not, yet it was the oil level that was problem causing rough idle and naff acceleration at times.

I know a LS is not a Renualt, but worth checking.

[cornershop]

Check your temp sensor:

https://us.lexusownersclub.com/forums/topic/75957-1998-ls400-ect-sensor-removal-engine-coolant-temperature/

[runsgrateasanut]

On 10/10/2018 at 12:46 PM, cornershop said:

I’m no expert but I’d start checking the battery at idle, make sure the alternator is charging.  A duff battery can generate lots of issue.

Not got an idle issue, but interested to know if my Battery is sound.  Checked pre-start at 12.5v and rose to 14.68v after start up, at cold idle.

The Battery was new less than two years ago, but the Car having had a failed Alternator 2500 miles back, and the Battery being jumped to get it in my drive after truck recovery, I wonder if that "jumping could have killed a cell?  

12.5V seems a bit below par for it standing? Only did a short journey Friday and any security drain should only be small. 

Opinion welcomed.

 

[cornershop]

8 hours ago, runsgrateasanut said:

Not got an idle issue, but interested to know if my battery is sound.  Checked pre-start at 12.5v and rose to 14.68v after start up, at cold idle.

The Battery was new less than two years ago, but the Car having had a failed Alternator 2500 miles back, and the Battery being jumped to get it in my drive after truck recovery, I wonder if that "jumping could have killed a cell?  

12.5V seems a bit below par for it standing? Only did a short journey Friday and any security drain should only be small. 

Opinion welcomed.

 

Various sites suggest that 12.5 is anywhere between 75% and 90% charged - maybe an overnight charge would top it up - the 14.6 is about normal at idle

[runsgrateasanut]

I suspect it will never charge to 100% as I ran it to almost nothing from QE Bridge to the 24 hour service stop outside Dover whilst it was not charging. Funny thing however,  the Battery charge light never came on, just the Wipers slowed almost to a stop. So, it probably Sulphated beyond remedy.  This said it starts first time and the last Yuasa Battery lasted the Car seven years, so I'll just monitor its starting. Last one died when I left it at the Ariport for two weeks with security on. If I do that again it would probably die.

[stericker]

Update on 'check engine'. Took the LS400 to my local indie (7 mechanics). They could

not find anything showing on OBD using the blinking method. I have been using it for the

last four days and the problem appears to have righted itself. Touch wood.

[Cotswold Pete]

Wonder if could have been some cr*p in the fuel that caused a hiccup, fingers crossed that it does not re-occur.

[stericker]

Pete, I think you might be right about the fuel because the problem seems to have gone away (fingers crossed)

after refilling with petrol. Surprising as it was BP.

[Cotswold Pete]

On 10/19/2018 at 10:03 AM, stericker said:

Pete, I think you might be right about the fuel because the problem seems to have gone away (fingers crossed)

after refilling with petrol. Surprising as it was BP.

Most petrol and diesel tanks at  garages will have a small amount of water in them (some more than others).  Usually not a problem, as even when I worked in a garage many moons ago, it was by a river and subject to flooding now and again, and we would have to check for water ingress, and never had a problem.

But looking on Web plenty of reports of water damaging engines. 

Fingers crossed that is all it was

[BigBoomer]

A big problem with modern "eco" fuels is Ethanol. This is added to all 95RON and some 98/99RON fuels to make them "greener".
The problem with Ethanol is that it attracts water and holds it in suspension in the petrol.
If too much water gets mixed in with the petrol you will get rough running and poor fuel economy.
In the pre-Ethanol days the water in the tank at the petrol station would settle to the bottom and could be drained off.

[Guest]

Bp ultimate is ethanol free. Lucky for me they just opened one 5 miles from home.



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