karmaz

Howdy folks,

First post here after lurking a long time, researching my purchase.

So I went and bought a 2004 LS430 which I absolutely adore. However, the MPG has been pretty disappointing.

The car has 95k, and a full Lexus service history (belt and pump done thankfully), and is running nicely with no apparent issues.

However, on a Motorway run (here in Ireland) i'm getting in US mpg terms (different from the UK measurement), a pretty poor 20mpg (even sitting at 60mph on cruise). City driving takes this down to 13mpg. I drive the car real gentle too, so it's not a case of a heavy right foot.

I was under the impression that the car is capable of much better mileage than this. My old e38 750i v12 was much better on fuel than this (especially on Motorway duties), and that only had a 5 speed box, opposed to the 6 on the LS430.

So naturally, for the next service (due in 2k), i'm thinking of replacing a few items to try and improve this:

Mobil 1 5w30
Oil & Air filter
8 x new spark plugs - Any suggestions on brand?

I was going to change the MAF aswell, but after going through the service history, it was only changed 2 years ago, so i'm a little unsure on this. It seems to new, and perhaps cleaning it is an option.

Anything else you guys could think of that would be useful to swap over with servicing?

Finally, the one thing i'm a little unsure of is, when the car is in drive, it idles like a dream, but when it's put into neutral, you can definitely feel it vibrate a little. Being new to the car, i'm unsure if this is a point to be concerned over?

Any advice greatly appreciated

xsbc63x

my car city mpg is about 19-20, if its a solid highway run ill get about 27 with the 10%ethanol gas we have here. If i happen to find some gas without ethanol ill get about 29-30 highway.

my car will get a slight shake in neutral - id say nothing to worry about.

check the oil, air filter, plugs id go with lexus, or ngk. clean the MAF and the throttle body and reset the battery(leave the cable disconnected for 30mins or so to let it relearn how you drive). could be an o2 acting up, but if theres no engine light on, may be hard to troubleshoot.

chicov8

13-15 mpg in the city and 25-30mpg highway (in gs430 but its same engine)
clean MAF and TB, as for spark plugs use denso or ngk

karmaz

Thanks for the responses guys. I'm going to clean the TB and MAF with the battery reset first, and then move onto the service items.

Kansas

Your fuel economy doesn't seem all that inconsistent with U.S. government ratings and statistics for the 04 LS430 - see attached - considering that your LS430 is substantially heavier than the average U.S. market LS430 assuming my understanding is correct about the LS430 sold in Ireland and the U.K. having standard rear air conditioning, power back seat, rear audio controls, etc.

It probably doesn't help that you are paying the equivialent of over $10 per U.S. gallon. Petrol prices just rose sharply here in the U.S. but I am still paying about $3.50 per U.S. gallon (91 octane). Americans would "freak out" at the prices you are paying.

warminwisc

No shakes from my LS neutral, park or drive. I can get even up to 30 on the freeway for long stretches at 70 depending on wind, etc. Good luck

Jabberwock

No shake at all from my engine, actually it is difficult to tell its running at all at idle, in gear or not. Have the shop check for any codes - like others posted make sure you have clean air filter , clean MAF, and cleaned the TB intake. Make sure tires are inflated to spec. Run a couple of bottles of concentrated fuel injector cleaner thru couple of gas tanks..not sure if they they Techron concentrate locally but sure to have some equivalent.

Your car should have a real time mpg indicator - I'd check at at constant speed like 60mph with and without cruise control on a flat surface - you should be seeing 27-35 MPG instantaneous readings. Anything consistently lower indicates some problem. Its a long shot but ask shop to check your wheels, calipers and bearings - to insure nothing is pulling or dragging. Also look for loose or cracked vacuum hoses, plugged hoses - and weird mods or accessories that may affect engine or add friction.

ippo

Have you tried to calculate the mpg yourself? Drive a bit with a FULL tank and reset the odometer and then refuel it. That way you know how many gallon you used for the given mileage.

Maybe your readout is not accurate anymore.

BigBoi94

Make sure the pwr button is not on when your driving, that make you lose fuel fast.

cpcc

Make sure that you dont have a rusted or partially seized brake caliper.

CurtAZ

I recently bought an 04-LS and notice quite a drop in mpg (from 25-26 to 20-21) once I had the tires rotated and alignment done. The shop said that it looked like the original owner hadn’t bothered with rotations and the tires at bad wearing and radial pull. I’m guessing the tires are now making the engine work a little harder. I’m looking forward to getting new tires to see if, in fact, this is the case.

Good luck!

AlexusAnja

This is strange that making the tires now "correct" would cause a drop. Usually it's the opposite that misalignment and out of.balance causes lower MPG. How are you measuring the MPG?

CurtAZ

I use both the dash display as well as calculating it manually at each fill-up. I could be wrong but the way I think of it, the alignment was off, and the tires had gone so long (at least 10-15k miles) without being rotated that the tires have worn in a “wrong” way. The alignment has been done and the tires rotated but that wear pattern is still there almost trying to pull/push the alignment back into its “comfort spot”.

Again, I could be completely off but that was the only variable at the time and it was a pretty drastic change.

karmaz

So a bit of an update. I had the car serviced, with new plugs, air & oil fiter, and cleaned the maf (I haven't got around to cleaning the TB yet, but will do). Also did a battery reset. Mechanic ran the codes, but nothing showed.

Anyway, after the service the car doesn't have any shake at all in any gear, parked or not, but MPG remained the same, if a small bit better.

So I tried a little experiment the other day. I decided i'd do my usual journeys, by putting the car into manual mode, in 6th year, and leaving it like that (it's fine to take off in, due to the torque)

Result: from 13mpg city to 15.5mpg over the course of two days.

Quite pleased with that result, i'll be driving like this from now on.

jayclapp

I just can't imagine driving an LS430 intentionally like a slug for a measly 2.5 mpg gain. Just my opinion.