Hi folks,

I'm a new member of the forum but have been reading it for years. I have a 2002 LS430 that I've owned since 2006. Other than an O2 sensor, I have never had a minute's trouble with her. However, it has recently began a problem: anytime you attempt to accelerate from idle, there is a one to two second hesitation (dead spot) before it will accelerate. It doesn't matter how far the throttle is opened or how quick. If I floor it, it will hesitate, then back fire a couple of times, then eventually take off and accelerate quickly. I have installed new spark plugs and cleaned the mass airflow sensor and throttle body but no help. The ECU shows no fault codes. I have always used 91 or greater non-ethanol fuel in it as it is parked most of the time (not my daily driver).

The only thing that I can guess could be the problem is that my sister-in-law borrowed the car several months ago and, ignoring my direction, she put 87 octane fuel with ethanol in it. I plan to drain the fuel she put in it and replace with higher octane non-ethanol fuel. However, I am wondering if any of you folks have had a similar issue with your LS.

Thanks in advance for any advice.

TOORED

 

ive been running 87 octane in my LS430 for about 5 years now, with no ill issues so I dont think it's that.

does it do the same thing while sitting there in park, or only while driving? I'm wondering if it's transmission related?

 

Thanks for the reply. It idles just fine. The transmission seems OK. If it were that, I would think that the engine wouldn't stall, then backfire upon acceleration. My issue with the 87 ethanol fuel is that it has been parked for a couple of months where the ethanol may have had a chance to turn to sugar somewhere in the fuel system. In daily driving it wouldn't be an issue because the ethanol is constantly being heated up and burned.

 

Does it run fine after that even at full power? Seems the fuel would restrict that also. It does seem like fuel problem at first.

 

If you have a scan tool capable of it watch active misfire monitors. I was having an issue where at idle or coasting I was getting misfires. It wasn't enough to trigger a misfire code to be saved in, but it was enough that I could catch it while watching the individual cylinder misfire counters. Then I was able to swap the ignition coils around and see that misfire moved confirming it was an issue with the coil.

 

I highly doubt it's because of the lower than recommended octane gasoline. How many miles do you have on the odometer? Sounds like you replaced the plugs because of this issue or issue. Hopefully you used Denso or NGK?

Personally, I'd replace the MAF sensor if you never have. It doesn't last forever!....and also spray the $H1T out of the throttle body AND "idle ports" with carb or fuel injector or throttle body cleaner or similar.

This is a great thread that should help you. A LOT of info on it!

https://www.clublexus.com/forums/ls-...-cleaning.html

 

What have you been doing to maintain the fuel injection system? (Octane has nothing to do with that, or ethanol vs. not).

If it has not been maintained, I would run a bottle of either Techron, or Gumout Regane High Mileage through it to start. Preferrably in-town driving or mixed, not all highway. Gumout has a slight nod in this situation per PEA content, but Techron is good. Redline FI cleaner is ok. One of these three, not the cheaper/less effective stuff.

 

Thanks again folks for the help.

I replaced the plugs with NGKs of the same part number as the originals. It has 150K miles. I run Techron in the tank at least twice a year but the car only gets driven 2K to 3K miles per year (it's mostly a garage queen). I cleaned the MAF sensor with CRC to no avail so I ordered a new Denso unit from Rock Auto. I will update if it helps. I suppose I will forget about the ethanol issue. I have read the tune-up thread by STANVANDAM and will try that if the MAF doesn't help.

 

Can confirm it does work funny enough, just used 3 treatments of the Gumout HM on the new DI 12cyl and it solved intermittent misfires on 5 cylinders.

Drive heavy though, helps to force longer injection times

 

If the car sat for months with Ethanol in the gas then it has probably absorbed a lot of water into the gas and will run bad.
I would recommend draining the gas unless the tank is nearly empty, and fill with decent gas.
If nearly empty fill up with quality gas and add some IsoHeet or similar water removal additive.

 

Backfiring and hesitation typically point to a lean misfire — your car isn’t getting enough fuel when the throttle is suddenly opened. I’d prioritize: 1. TPS voltage tracking. 2. Fuel pressure test. 3. Smoke test for vacuum leaks. 4. Coil-on-plug test under load.

 

I had some hesitation on turns (slowing down then reaccelerating), but it resolved itself. This was years ago. The backfiring thing does not sound good. The good news is that you are getting this consistently. I use 91+ gas but have on occasion 9in the past tried a full tank of 87. Zero discernible difference.
I often hear people say to disconnect the battery to cause a trans relearn, or other computers. It probably cannot hurt. But I think you need the car diagnosed. I doubt it is the gas, from my own experience. Many people use 87 for years.

 

I want to apologize for the belated update; I've been very busy the last two weeks.

I replaced the MAF sensor with a Denso unit from Rock Auto and it seems to have fixed the problem. Hallelujah!

I want to thank everyone who responded and offered advice. You folks are the best and I greatly appreciate the help.

Thanks again.
TOORED

 

I suspect that the problem is caused by the voltage glitch caused by the failing APPS (Accelerator Pedal Position Sensor).

The ECU needs more than 2 seconds to judge the failure of the glitch to last. At the initial stage of the failure of the APPS, the glitch only last just a very short time and the error code is not stored but the injectors reduce the injection in accordance with the glitch.

One method to confirm this is to measure the voltage using an oscilloscope. Another method is to increase the engine RPM extremely slowly. For an example, slowly push the accelerator pedal spending for more than 30 seconds to increase the RPM from 750RPM to 2500RPM.