badazzz06

So after two years of searching and trying things and visiting Lexus service I am becoming frustrated with this hesitation / bucking problem my 2001 gs430 is having without throwing any codes. It occurs sporadically (much more in hot weather) under very light throttle while cruising, at takeoff from a stop, or even at idle. While at one of the better Lexus service centers in my area they couldn’t figure it out after having the car for two weeks. They checked for codes, tried a different MAF, tested the throttle body, said the cats weren’t clogged, and said the o2’s didn’t show any problems, and replaced the plugs. But the car still has a dip in the power curve where it runs lean. When talking to the tech the only other thing he could think of was replacing the ECU but that would be $$$. I don’t want to just throw parts at it that aren’t throwing codes as being bad ie. o2’s or ECU.

Please let me know any ideas you may have of what to test or replace.

Here is a list of what I have tried / replaced:
1- Pedal position sensor
2- MAF meter
3- PCV valve
4- Fuel pump and filter
5- Driver side oil control valve
6- Plugs
7- Checked for vacuum leaks
8- Removed an aftermarket intake and return it to stock
9- Tried running for a year with an oil separator on because some oil passes the PVC valve
10- Cleaned the MAF and throttle body numerous times
11- Cleaned upper and lower intake manifold
12- Sea foamed the system 2 or 3 times
Also replaced a fuel injector and ignition coil on separate occasions but were unrelated to this problem.

wise2k

I had that problem, but mine actually threw a 'running lean' code. Went through MAF sensor, and the like even took it to Lexus of Louisville (have a thread on here) where they couldn't even figure out what it was but tried to charge me.

Long story short, it was the fuel pump. Replaced that and all was lovely!

SaiyanGS3

iTrader: (8)

throttle body sensor gone bad?

blueman26

I've been having the exact same problem for the last two summers, going on the third this year, with my 2004 GS430. Problem disappears during the fall, winter, and spring. Will be taking it to Lexus for the 3rd time in as many years next week. I’ve pretty much resigned to the idea that whatever fixes the problem is going to cost a ton, so it would be great if it was just a fuel pump, as in wise2ks situation. My post is “summertime cold-start hiccup/stumble”.

GS4_Fiend

iTrader: (22)

need some scan data parameters to diagnose this. tell us what you replaced doesn't help.

wise2k

Before stating that I replaced the fuel pump I mentioned that mine threw a code relating to the engine running lean, specifically it was P0171. I started a thread on here about the dealer's failure to diagnose, and here it is: https://www.clublexus.com/forums/gs-...-diagnose.html
I hope that helps some

badazzz06

Any more suggestions ??

vijayn

Hey bud

Do you have access to a multi-meter? You can check the O2 sensor your self. All pre-cat O2 sensors should be check for correct voltage and response time.
At idle and fully warmed up, the O2 sensor signal wire should be cycling between 0-1V DC, you should see around 8 - 10 cycles per 10 seconds. When you give a quick rev to the engine, the voltage should go rich (near 0.9-1V DC) every time you give a quick rev.
If any of your pre-cat O2 sensors dont go past 0.6 -0.7V at a "rich" event, then it needs replacing.

Also check around the HT leads and coils for traces of tracking. Give them a good clean if you see any residue and check for proper resistances.

blueman26

Because it sounds like we might have the same problem figured I'd post the same response in this thread also.

Lexus dealer suggested the first thing to do was clean the TB with a "new" product from a company called MOC. The drive home from the dealership was smooth, but the next morning the problem was back although it wasn't as bad. The two diagnostic techs that worked on the car recommended replacing the throttle position sensor if the cleaning didn't solve the problem. Will be taking the car back after the holiday.

SaiyanGS3

iTrader: (8)

Exactly what I said on 6/21.

SC400slide

iTrader: (11)

TPS, o2 sensors, and also could be the ECU. I think these issues would be most likely caused by o2 sensors. I had the symptoms, and I replaced them, and that fixed it.

ThomasGS4

iTrader: (19)

I'm truly hoping this is my fix as well, as I am experiencing the same symptoms you did. The only code I am receiving is P0172. I have tried a brand new OEM MAF with no luck, and the O2 sensors seem to be performing as they should. Will be checking the fuel pressure here shortly.

blueman26

Yesterday I turned the ignition to “on” without starting the engine, let the brake booster run it until it stopped, then floored the accelerator pedal several times, and started the engine. The problem didn’t show itself. Tried the same thing again this morning and got the same result. It’s been a week since I drove the car but will try to go out today and see if it hiccups on the road. I have an appointment on Monday to replace the TPS and do a power steering flush.

Would be curious if anyone else having similar symptoms might have the same result?

burny

just replaced the fuel pump and filter and hopes this stops the hesitation. Filter was extremely clean, but the pump could have been failing. No codes were ever thrown.

badazzz06

Sounds odd but I’ll give it a try on the way home.
Plus I also remembered recently how much it clears up if the weather is below mid 70's