Lumpy Idle, Stalling, Engine Light On...?

[AdeV]

A few days ago, I stuck 20 quid of fuel in the tank, and shortly afterwards (maybe 10 miles?) I started experiencing lumpy idling, cutting out at lights, and the EML coming on & off. Assuming it was just some water in the fuel, I went for a run up & down the motorway, which seemed to cure it. I ran it until maybe 10 miles after the fuel light came on & put 20 quid more in from my usual garage (not the suspect one). However, the lumpiness has returned, even more so if anything, and now the EML comes on even if the lumpiness doesn't appear to be present.

Power output seems unaffected, the engine still revs freely, and under hard power ( ) all seems well - same at motorway speeds. However, she's become a nightmare to drive around town.

Any suggestions as to a fix? Do I just need to ride it out, run the tank as empty as I dare, then fill up to the brim with good fuel? Or some other strategy?

Also, the EML thing, am I right in thinking that's now an MOT failure? If so, I need to get it turned off. I'm competent around computers, and with the correct cable & software could get the fault codes & reset the light - but what s/w & what cable, is eBay my friend here or does someone have a recommendation?

Cheers!

Ade.

[andy m w]

cold weather ? highlights problems with MAF,s or coil,s ,

you can fill up with quality fuel but more than likely fuel not the issue ? the computer on board will adjust to a certain level to accommodate different fuel quality , what miles have the plugs covered ?

[beavisrules]

The dash light will go off by itself when the problem is fixed.

stalling LS have commonly been dirty throttle body.

could also be sensor/electrical, o2 sensor/temp sensor/coils/leads etc.

pretty sure the mk3 & mk4 are obd2 and so normal cheap fleabay obd2 lead & software should work (have a feeling you need one that can read CAN bus).

the error codes should give you a hint of the problem.

[AdeV]

Thanks for the replies chaps...

The lumpy running started before the weather went cold; the cold may be exacerbating it, but it's not the cause. Also, the rapidity with which it came on (i.e. it's never happened before, and suddenly it's full-on) would tend, I think, to rule out dirty throttle bodies, etc. I changed the plugs less than a year & less than 20k miles ago. I couldn't rule out the coils as I've not changed those in my ownership.

My car is the Mk2, is that still compatible with the OBD2 cable? There's a diagnostics plug atop the engine, but I know nothing about car ECU systems...

[beavisrules]

mk2 is definitely not OBD2. and will need a proprietary reader/adaptor.

I think the following link *should* apply to you.

http://www.lexls.com/tutorials/intro/codereading.html

[Ruud]

I have a friend in Canada which had this exact same issue. He changed coils, plugs, wires and cleaned TB and it made no difference at all. It turned out to be the engine ECU. He bought a 2nd hand one and she ran like new again.

This might not be the culprit in your case, but I thought I'd mention it.

[AdeV]

Hi Ruud,

Looks like you might be right :(

Yesterday I had to drive 200 miles to Scotland. About half way up, I noticed the occasional bump (at around 2900-3000rpm). The engine light was on all the way; however - as before - the long run seemed to cure the rough idle.

Today, on the return trip, no engine light or idle roughness, but after about 5-6 miles, the engine began to hiccough both severely and at higher rpms. As I was still nearly 200 miles from home & have no breakdown policy (this IS a Lexus after all....) I persevered. Accelerating was a very dodgy affair with the engine coughing and lurching very badly, but once up to speed she wasn't so bad. Worse on the hills, i.e. this problem definitely manifests under load. 200 miles and some kangarooing later (worse at the end of the trip) I have arrived home - even when badly sick, it seems nothing will stop the LS400... Interestingly, the EML light is no longer lit, and the idle roughness appears to have completely gone; but the high-speed lurching and outrageously bad acceleration mean the car is basically on sick leave now until fixed or replaced. I'm going to try the coils & ECU as a first stop; plugs & wires I'm happy should be OK. My biggest concern is that I've knocked years of life out of the gearbox, some of the lurches produced some noticable bangs from the back axle...

[steve2006]

Did you pull the diagnostic codes when the EML was on using the jumper wire method and then count the flashes as per the Lexls link?

Just changing parts without proper diagnosis costs time and money.

Going with the fuel top up and start of the problems when was the fuel filter last replaced?

Check to see if there are any stored codes then go from there all you need is a piece of wire or a paper clip.

[AdeV]

Right... I;ve done the wire thing, and I'm getting code 13 (RPM Signal No. 2).

I don't have a repair manual, so if anyone does who's willing to look up what that means & what the next steps/fixes are, I'd be properly grateful, thanks in advance!

[steve2006]

I googled "Lexus LS400 RPM signal no.2" and there were pages of information some very good from forums and some absolute rubbish like fixya.com!

There appears to be various causes including the cam sensors and wiring ( the serpentine belt can cause chafing to the wiring to them if not correctly dressed), the spark plug leads, the ignitors and a slipped timing belt ( a tooth or more out)

All these are fairly easy to check visually apart from the ignitors but even here the wiring and connection plugs to them can be examined,disconnected,,sprayed with some switch cleamer/WD40 and reassembled.

[AdeV]

Must admit, I'd considered changing the coil packs (aka igniters) when I did the plugs/leads, but didn't bother. Is there an easy way to find out if one is flaked, without getting electric shocks? I'm thinking maybe an oscilloscope could be used here...

[steve2006]

An oscilloscope would be OK for checking the primary LT side of the coils but not for the secondary HT side at around 30KV!

If you are unsure they are not expensive from Sutton Autofactors and it is normally the passenger side one that goes.

Another tip is to start the car up in darkness then have a look around for arcing on the coils and HT leads.

Did you check the wiring loom around the front engine sensors?

[AdeV]

I borrowed one of those widgets that has a flashing light on it, which lights up every time a spark goes past. Testing was inconclusive (couldn't really see much change when the engine missed). No visible arcing around the coils, I haven't taken the covers off yet to check out the individual leads down to the plugs. I tried using the oscilloscope to see "through" the insulation, but the signal was too noisy to be useful. You could see it moving when the engine missed however, which at least means it's definitely electrical (which I think I knew anyway). So.... possible faults are coils (or maybe multiple plugs/ht leads; the plugs are proper NGK Iridiums, not sure who made the HT leads, they all came from America), ECU or LH cam sensor (or wiring to that sensor).

I've temporarily worked around the problem by buying another car :) Another LS 400 naturally, Mk4 this time.... will post some pics elsewhere soon.

[steve2006]

I like your method of working "My LS developed a misfire so I just bought another one" :D

[abs66]

Its probably cheaper to buy a new one rather than replacing all the parts lol.

Everyone seems to be getting all their parts from the USA , I've heard RockAuto are good anyone use them?

[Rupert Dubreaux]

Slightly off the topic but in reply to ,abs66 regarding RockAuto . I can recommend them ,I have used them twice in the past year, both my orders arrived within four days. They do stock some parts that are hard to obtain here and their prices are competitive even with the postage costs ,my last order for plug leads ,rotors and distributor caps came to £74 inc postage, all the items were of reasonable quality no Chinese junk .They also send you a monthly newsletter which can be quite interesting and will email any offers on parts for your car .

I have been a member on here for over a year now since I bought my LS and would like to say a big thank you to all the members whose posts have been very helpfull in keeping my beast in good order.

[abs66]

Thanks for that info Rupert its always good to hear feedback about a supplier you are thinking of using. Cheers.

[Thunderchild]

Hi, I've also used Rock Auto and can echo what has been said already. Great guys to deal with and definitely cheaper than buying here in the UK. Fast delivery and spot on items!

Tc

[AdeV]

So I finally pulled my finger out of my ar$e and bought a couple of coil packs - which haven't fixed the problem :( So, ECU next; does anyone know the part number for the 94-96 models (that is, the Mk2, NOT the Mk3.... or the Mk1). So far, all I've found is '89-'94 or '97-'00 codes... or North American ones

Duh, got my model years all screwed up....

IIRC: Mk1 was '89 to '92?

Mk2 is '92 to sept '94

Mk3 is Sept '94 to 1997(not sure when)

Mk4 is 1998-2000(01?)

Also, where _is_ the engine ECU on a '95 Mk2?

[steve2006]

The ECU is located under the passenger side glovebox.

Along thread off another Owners Club but may help you with the ECU.

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

[abs66]

Thats a very interesting read Steve. Am I righ in thinking that our climate over here is a bi more friendly to these capacitors or is it likely our need doing to?

Heres the big question, does the club know anyone who can do this over here?

Cheers

Pete

[steve2006]

I have done several LCD climate control displays including my own and the flashing speedometer clusters so the ECU capacitor repairs would be on a similar scale for me.

Mind you 30 odd years in the industry does help :D

The capacitor problem is widespread throughout electronic equipment due to the design and quality and affects most domestic electronic appliances to some degree. With design improvements more suitable reliable capacitors are now available for ECUs made 10-20 years ago.

Industrial and military items are generally made with higher grade components to start with as pricing is not an issue.

Now how many members have had an LCD TV stuck in standby or completely dead to be told the capacitors have gone? There will be a lot of you.

[abs66]

I was really tempted to replace my capacitors anyway after reading all those pages but although I'm reasonable with a soldering iron I think I might just give it a miss bearing in mind I NEED my car on the road.

Mind you a man of your caliber might be able to make a few bob doing this job.

Do have a price in mind?