4blizak4mn

Fuel filter is attached to the fuel pump inside the tank - it's a strainer style filter that's about 4 inches long. Agreed on logical diagnostic process, but I think we may have solved this one:

I went through all engine compartment connections to rule out something being loose with either electrical or vacuum system. Only thing I could find was that last time I cleaned off the MAF and throttle butterfly plate, I apparently hadn't tightened down the metal band that secures the air intake tube to the throttle body. A rubber gasket on it holds it there tight enough that it doesn't move, so wouldn't be a problem right? Apparently not. Tightened it down, haven't had a problem since in 2 days of driving.

Here's what I think happened: Fuel/Air ratios are impacted by two things, a combination of sensors (MAF for intake air, O2 on the exhaust to confirm proper combustion) and the throttle plate (which regulates the actual airflow into the engine). When the engine is under light load it draws slightly more air to match increased fuel consumption, meaning the throttle plate opens slightly. If the MAF reads a certain volume of air, but more was coming in around the intake/throttle gasket under light load, then you'd have normal readings on the MAF but increased readings on the downstream O2 sensors, which would make the ECU think the mix is too air rich - and it would rapidly close the throttle to correct this. I think that's what I was feeling.

Anyone care to confirm if this seems right? Thanks again to everyone for all the help!! Hoping this is truly it.

kjcole

Nice find. That saves a ton of work

mrblister

Pilot error . Happens to all of us,

4blizak4mn

amen to that. Just hoping that really IS what happened and that it hadn't just been behaving nicely for two days . By the way, changed out the fuel filter last night. Not too hard and will post photos shortly on a separate thread.

4blizak4mn

Hi all, so the odyssey continues. The throttle problem came back shortly after my last post and I've done some more work to try and fix it. Removed the entire throttle body and cleaned everything (worth doing on your vehicles - I was amazed at how much carbon was in the idle orifaces - way better idle/performance afterward). I also replaced the accelerator pedal position sensor and MAF. None of these corrected the problem. The problem has also manifested itself at cold start idle which is new. Had a shop I trust look it over and they had no clue but saw the exact same symptoms. Recently it's started to smell like it's running really rich which makes me think it could be upstream O2 sensors too. Going to replace the throttle position sensor again (to rule out a faulty replacement part as symptoms started a week or two after I replaced this) and then probably move on to O2 sensors. Anything else you all can think of?

LexBrett

I think you have done most of this already, but if it were me I would:

clean throttle body
clean MAF
Run Seafoam in vacumm line
Run Seafoam in gas tank
Change ATF and put Lucas additive
replace spark plugs
check no vacuum lines disconnected
check for CEL codes with OBD2 reader

=just my 2 cents let me know how it works out

4blizak4mn

Have tried all except for running seafoam in the vaccuum lines. Where did you start the siphon for that? Would you mind sharing? Should be an easy thing to try tonight.

Also as I did some research, it looks like the water temp sensor has a significant impact on timing in this vehicle (ECU advances timing if coolant is cold). This problem seemed to start in around mid-October when it was getting cold here in MN, so I'm thinking that it could be caused by that sensor. It's $16 so may be worth replacing too.

LexBrett

Do you mean the engine coolant temperature sensor? I also changed that because I was getting a code. It may not be your problem but is worth changing.

You can go through the PCV valve to run the seafoam. I have a thread with instructions. Feel free to PM if you need help.

4blizak4mn

Installed new PCV last night and have not been able to replicate the problem since then. May have fixed it, but then again it's gone quiet like this before.

I also used seafoam on the PCV to Throttle body vacuum line. Smoked like a wildfire, but a significant improvement in low end torque.

I was planning to test it out today before I snapped off a valve stem filling the tire this morning. For future reference, don't snap off valve stems. They're apparently proprietary to Lexus rims and cost $80 a piece. Really???

I"ll keep yall posted.

LexBrett

Good to hear changing the pcv helped! And seafoam is great stuff.

Don't panic if you get a misfire code after the seafoam. I think that's because carbon gunk was freed up. Just run the car hard on the highway for about about an hour.

$80 valve stems? I get mine for $10 at merchants

bhop

blizak...you have changed out or adjusted just about everything including the kitchen sink..........except you haven't done the fuel pump from what i can see, unless i missed that in one of your earlier posts. i'm stuck on the fuel pump as you can tell...

kjcole

Valve stem is integral to the tire pressure monitoring sensor. So you'll need to get a dealer to make sure the new sensor is talking to the car's electronics

LexBrett

Oh I took out the tire sensors years ago. They are so delicate and expensive to repair. I'm much happier running normal valve stems!!

4blizak4mn

Yeah, it's a daily driver so when my mechanic said there was only one valve stem left in the city I wasn't in a position to argue. . Original lexus part too because it's finicky as mentioned.

SO. I think we can call it officially solved. It was the throttle body sensor that I had replaced a few months ago. Part was defective. I replaced it with another one and its run fine for four days. I guess I hadn't thought that a brand new OEM part would be to blame but it definitely was.

That said the car runs great now thanks to all the other stuff I've done to it! Thanks for all the help troubleshooting this issue!!!

sleepinglh

what is a "throttle body sensor"?
throttle position sensor?
Have a link or photo to show?
I have same issue got a Throttle motor code but didn't get a chance to write it down before the mechanic cleared it and it never came back but the car is running lean and stumbling.

Thanks