Jittery Idle

[Stu76]

I have recently bought a 1993 LS400 primarliy thanks to this website.

I had been looking for an S-class merc, but then a Lexus turned up - something I hadn't considered at all. A few days hurridly finding out about them, mostly via this website, made my mind up at to what it should be worth and whether or not to buy. Silly decision really being as I was fairly clued up on S-classes and have been watching their market and been looking at auction since winter!!

Anyhow, one LS400 and a happy customer later and it's time to spend some money on it. It has 135k on the clock with a lexus service history upto ~126k which was in 2002. The chap I bought it off hasn't done many miles in it but also hasn't bothered servicing it.

So I need to sort it out before it gets too late and I put many miles on the clock.

Having come from a four cylinder engine I am not sure just how good these cars are supposed to be but I have noticed that when idling the car does seem to vibrate slightly, probably more than I you lot give me the impression that it should. When in a dealership last week looking for servicing prices I asked a chap there to come and see what he thinks and he said that it is a pot or two down at idle. I have returned 24mpg on the first tank I have used though so I don't think it can be running too badly at speed.

So what should I do? I think that it wants a cheap A service for now, so that I can get the book stamped and a general look around, but should I get the plugs done too? I tend to just think that this hides the real problem temporaryily - is that right and if so what else could be up?

Also looking for advice on the wheels. It have wheels from a 200 on it has the last chap said the proper ones were fairly pitted so when he was ready for new tyres he just bought some new wheels out of the autotrader. I personally think it looks great, especially as the alloys on LS400 have always been a bit ugly in my eyes. But does this make my car look silly to a real Lexus fan??

Once I work out this website I'll stick some photos on....

[maneesh]

dude,

congrats! first thing is that there should be NO engine vibrations on a LS400. Given your mileage and age, I would suggest that the engine mounts and/or transmission mounts are worn/split. Essentially, these are pieces of rubber that are designed by Lexus to absorb the vibration from the engine and transmission. Everyone I know with an old LS400 exhibiting vibrations has said that replacing these mounts brought the "as new" smoothness" back. Can you feel any vibration when sitting in the car at idle?

[PhoneDrome]

Let somebody have a look on your spark plugs. Begin with the last cylinders.

Think a bosch service can do this with a oscilloscope. Also let them hav e a look on the compression.

[MartinShorthose]

I have just had my first service done on the LS400 complete with cambelt change.

One fault that was pointed out to me was some chaffing of plug leads.

I don't know where this occurs but they kindly replaced four for me (at vast expense).

This might also be something to check.

My tickover speed is a little lumpy when the aircon kicks in and out but apart from this rise and fall in revs occasionally, you should be running totally smoothly.

Incidentally, I was sitting in my parked car listening to the end of a Radio 4 broadcast that I had become fascinated with.

All of a sudden I thought I felt a slight earth tremor - a very slight movement of the whole car.

It happened a second time a couple of minutes later and I turned the radio off to concentrate, thinking I had felt a small earthquake!

I then turned off the fan to make it quieter still in the cabin.

It wasn't until a couple more minutes had passed that I noticed that the aircon was on and that this could not happen unless the engine was running.

My earthquake had been the shift in engine revs when the aircon came on.

I hadn't even noticed that I had left the engine running - that's how smooth this V8 should be!!!

[flotsam]

I asked a chap there to come and see what he thinks and he said that it is a pot or two down at idle. I have returned 24mpg on the first tank I have used though so I don't think it can be running too badly at speed.

You must know that the S-Class actually shuts down some pots for economy. I've run a four cylinder on 3 pots before and it seems to run ok, if a little rough.

[ROYT]

hi!

I would start with a new set of plugs if little or no recent service history

is known.

If no cure, next .....new HT leads, both positive jobs to do.

OEM plugs are iridium I beleive and expensive but standard plugs are available.

On my'94 LS you can stand an old style threepenny piece on the engine

when it's running and it won't fall over....yours should be the same!

cheers ;)

[ColinBarber]

OEM plugs would be Platinum at that age.

[maneesh]

I think it's something like 160 quid from lexus for all 8 plugs!

120ish for the leads!

[ColinBarber]

Hopefully people aren't paying that money for plugs. I got my last 8 (better than the OEM plugs) from eBay.com and cost, including shipping to the UK, about £42.

[Chris Skelton]

Colin: let us have more details on your plug source? What type/kind were they? Where from (site address? etc.) All helps in our ongoing life as Lex owners.

[ColinBarber]

Actually I think it was closer to £50 but still a big saving over UK prices.

I got Denso iridium Power plugs. They are a performance plug so don't last as long as the OEM ones (need to be changed every 30k miles) but I instantly noticed an increase in mpg even though my old plugs looked fine and had covered less than half the recommended distance.

The correct model for my car, and also for the 4.0 V8 engine, are IK20. Do a search on www.ebay.com for IK20 and you will find a few different people selling them.

Brought mine from a member called sparkplugssource. $35 for a pack of 4 and he charged $15 to ship 1 or 2 packs to the UK and I received them within 5 days.

[PhoneDrome]

So did I. I'm very happy with the IK20s. LINK

[andyhart21]

I think the OEM Lexus plugs are made by Denso anyways........ they are on the IS.

Like Colin says, switching to the iridium plugs from the Platinum ones, you should see a slight MPG increase.

[PhoneDrome]

Sorry a little off topic. I had NGK IFR6A11 as OEM. Just changed them to IK20.

Lexus has Denso and NGK (OEM). Seems to depend on the year the car was build.

[ColinBarber]

I think the OEM Lexus plugs are made by Denso anyways........ they are on the IS.

Like Colin says, switching to the Iridium plugs from the Platinum ones, you should see a slight MPG increase.

Yes the OEM as normally Denso although they do also use NGK.

I actually swapped from OEM iridium to the iridium power plugs and noticed a difference.

[maneesh]

Extremely useful info Colin.

Oh well, I've already changed mine last year, no need to replace until 2008!

What difference in MPG do you get? If it's significant, I might replace the platinum with iridium now!

[ColinBarber]

What difference in MPG do you get? If it's significant, I might replace the platinum with iridium now!

Difficult to tell. I would say up to 1mpg (which is a 3% increase). Recently had a 200 mile trip up to Liverpool. Got 30mpg up (no aircon) and 29mpg on the way back (with aircon). Used to get 26-28mpg although I've also been using Optimax for the last 5 tank fulls which may have added 1 or 2 mpg.

The plugs definatly made a difference on the fuel computer. When I come off the accelerator the mpg goes to 99.9 and once the car slows to about 40mph it start to drop. As soon as I put in the new plugs the speed would get down to 35mph before the mpg started to drop below 99.9

[maneesh]

Difficult to tell. I would say up to 1mpg (which is a 3% increase). Recently had a 200 mile trip up to Liverpool. Got 30mpg up (no aircon) and 29mpg on the way back (with aircon). Used to get 26-28mpg although I've also been using Optimax for the last 5 tank fulls which may have added 1 or 2 mpg.

Hmmm, I used to be able to get 32mpg on cruise control at 70mph a few years ago. I struggle to get over 26mg doing the same driving now. I have changed my oil and filter every 6 months, and have stuck to the servicing schedule like glue.

I don't understand what could be causing the increase in fuel consumption. I've never used optimax though, just supermarket petrol.

[ColinBarber]

I cleaned the MAF sensor on my car and the mpg went up from 26 to 28 on a car less than 3 year old with only 26k miles on the clock.

Injectors could also be dirty, throttle body may need cleaning, thottle position sensor not adjusted correctly and as an engine wears it becomes less efficent.

[Stu76]

Thanks for all that info.

I have had the car in to the main dealers last Friday for an A-service, since the book was badly in need of a stamp. Due to the age of the car I couldn't warrant paying Lexus prices so I've let the book slip to Toyota (Bentley's of Warrington). Can't imagine that's too tragic.

The chaps there didn't pick up on the engine not running properly. In fact they had another 1993 LS400 in on the same day. It was even the same colour, chap told me that mine runs great so do I think I'm being too picky or do they not know what they are on about? They used to be Lexus dealers, and as I just said they had a benchmark on site to compare it with!

Not sure whether to bother with the plugs yet then. It sounds like I'm opening an expensive can of worms that doesn't really need fixing. I'll concentrate my money on the air-con and start to consider that cam-belt change which needs doing (5 years, 17 thousand miles - again do you bother?)

Oh by the way, Toyota reckon my rear pads need replacing - £100 all in, that the front discs want skimming (which I thought too) - £160, and a brake fluid change - £45. What about the front discs though? When I first got the car the pads had only done 400 miles and the car did judder quite noticeably under brakking, I've done about 1000 miles in it so far and it's no where near as bad. Were they just bedding in or am I getting used to it???

Stu

[ColinBarber]

You will be able to get the discs skimmed for much less than £160.