lisaB1

I need a little advice. Recently my 04 ls430 seems to be starving for gas on heavy acceleration. Mild to moderate acceleration is a bit slower but no sputtering. I had my mechanic put it on a code reader and "no codes came up, check engine light is not on, and the catalytic convertor does not smell nor is it hot hot. I did notice yesterday for the first time that putting my foot to the floor I hear backfiring like you would in old carbuerator cars along with the sputtering, Any ideas for me to focus on? I am thinking of chaning the fuel filters.
thank you boys for any help here.

Lavrishevo

iTrader: (1)

I would start with cleaning the throttle body and the MAF sensor. It's best to remove the whole throttle body when cleaning it. Make sure to replace the gasket with a new one. The MAF is right at intake air box. You can get CRC MAF cleaner at the auto parts store. Fuel filters are not known to be an issue on the 400 or 430 but it could also be a possibility.

MikeFoxx

iTrader: (8)

I had something similar on my GS. I had some oil on the spark plugs... Changed those and the gasket and i was running better than before the symptoms. MAF cleaning is always a good starting point since its cheapest and fairly common.

BradTank

I'm amazed something like backfiring and sputtering is not throwing any codes.

I personally would take it so a Lexus dealership and let them put it on a real scanner where they can go in depth to see what's going on beyond just "check engine" lights. Something like a $50 OBD reader is just not enough diagnostics and honestly if that's all your shop did, that sounds like a pretty hack shop to me. I would find a shop that has made the investment into real tools.

It's cheaper to pay a dealer a $100 or so to figure out what's going on before throwing parts at it. Changing the fuel filter would require dropping the tank, so i would definitely want to know what the real problem was before I tackled the project.

1WILLY1

iTrader: (9)

yea it sucks man , but you've got to have it properly diagnosed.

If your car is due for a tune up id do that along with the MAF cleaning, and see how that works.

If that doesn't fit it then id also agree to drop it off at the dealer if you don't have a trusted mechanic.

lisaB1

thank you all for your replies and possibilities. I will try them. I should say the my mechanic is one who works at my company and takes care of all our ground equipment. This was the easiest way to have him put on a scanner and see if there was anything coming up that I could do. I did use Tehcron fuel cleaner in 2 tanks of gas and there has been a little improvement. It is when I need the acceleration and put my foot to the floor that there is nothing and some backfiring under the hood like old carbs used to do. Thank you all again

MikeFoxx

iTrader: (8)

Lisa,

Make sure you check your spark plugs and wires... the backfiring if not fixed will eventually start to damage your cataytic convertors. As previously mentioned I had this on my GS and now that I'm reading it again I remember having the backfire issue on my 96 Impala SS. I put in new plugs, wires, & optispark. I was still having a missfire and after some tinkering found that one of the NEW spark plugs was no good. Got it all straightened out and it was like a beast came back to life... and then I got the code for bad cats thrown... put two new ones on and everything was green light from there.

GS - had oil in the spark plugs
Impala - bad wires and plugs

Both - resulted in loss of power/accelaration felt very sluggish

Riick

Your symptoms sound a lot like what turned out to be a bad MAF on my old 2000 Avalon.
MAFs have gotten cheap, since they now so common (?), RockAuto under $80 for OEM Denso unit.
I'd try cleaning MAF for a start, and if no joy from that, take it in for electronic diagnosis.

RA40

iTrader: (6)

How many miles on car? What gas is used and is the happening after a recent fill up? How is the gas mileage? How dirty is the engine air filter?

Other possibilitiy: ECT sensor. This is responsible for telling the ECU how to adjust the fuel curve relative to coolant temperature. High miles cars, this will typically show symptoms of excessive fuel consumption and a drop in performance. 10-12 MPG city and maybe 18 MPG highway. This is important because if it is dumping all this fuel and it isn't being burned properly, it will potentially overheat the cats. That is a very big $$ replacement.

An ECT sensor going south may not throw codes initially, it will cause a downstream issue with O2 sensors. Those also control air fuel ratios and the cats get the work when it goes south.

Along with MAF, check that any vacuum lines and wiring connectors are not cracked or disconnected.

lisaB1

Hi
I have 108k miles on the car. Im going to take it in this week. It runs fine, idles fine. accelerates when not pushed, but put your foot to the floor, and nothing but some back firing under the hood and no acceleration. No loss of mpg that I see. Sighhhh..... I will post here wen the problem is found

lisaB1

Hi, I took my car in and it turns out it is the maf sensor. They wanted $549.00(firestone) for the diagnosis, parts and labor to fix. I thought that was a bit much, ok way to much. I did some research and can get the part for less than 100.00 and it seems to me that I can put it on. looks pretty easy. so that is what I will do.

Riick

G_d bless & keep Firestone..... far away from me.
Labor involved in swapping the MAF on my last car involved 2 screws + the electrical connector .
My new MAF was good when I sold the car ... another 70,000 miles.

toantran99

I'm not saying it's the fuel issue but you DO NOT have to drop the fuel tank to change the fuel filter. Just take the backseat out, it's under the seat. I just had to replaced my fuel pump since my car won't start.

writes123

i've dealt with some hesitation issues in acceleration which some brands of gas. i always use octane 91 (highest available in CA. unfortunately no ethanol-free gas near me. i usually fill up with Circle K gas or costco gas.i've also used techron every 8 tank fills. just filled with a full tank of Shell V-power. no more hesitation issues for me. still have to decide if keep shell or chevron fills since they're about 10-15 cents higher per gallon vs the alternatives.

Lavrishevo

iTrader: (1)

In CA you may be better off buying some octane boost in bulk. Adding the ethanol to 91 lowers it even more and lessons your fuel economy and especially performance. Ethanol is such a waste.

Anyway, keeping that octane level high is ideal for our high compression V8's. The best power and mileage I saw in both of my LS's was with treated 93 octane. With the way knock sensors work the higher octane means the timing can be advanced to peak. Try it sometime. Measure your tank to run 96 or so.