GS4302001

On way to work this morning the LS400 (256,250 miles) started to cut-out while at around 70 mph. This was at about 15 minutes into drive (10 minutes at 70 mph) - the roads were wet and ambient temp was around 35F. Once I slowed down and attempted to accelerate again, it was hesitant to accelerate. It would cough and sputter and eventually "take-off" enough to allow me to make it to work (~2 - 3 miles on city streets). If I kept the pedal depressed, I am sure it would have died completely (had to feather it). However, when I floored it, the car would accelerate (I'm thinking not at top acceleration but, it went well past 60 mph (on the city street)). It was idling ok at ~750 rpm before getting to work, but it degraded to where it hardly even idles, now.

5 codes showed up:
PO171 - System Too Lean Bank 1
PO130 - O2 Sensor Circuit Bank 1 Sensor 1
PO133 O2 Sensor Circuit Slow Response Bank 1 Sensor 1
PO150 - O2 Sensor Circuit Bank 2 Sensor 1
PO150 O2 Sensor Circuit Bank 2 Sensor 1

I have been receiving intermittently over the last few weeks the code which says something about efficiency on bank 2 but it didn't indicate a specific sensor issue. I suspect all of the above listed codes are due to the throttle opening and not getting sufficient fuel. The fact it ran up when floored has me puzzled, though.

A little more info:
This is my son's car. It completely died on him 4 hours into his trip home from college last Thanksgiving. We kind of thought it was due to the fuel pump resistor based upon the symptoms he experienced. We trailered it home. When we first got it home, we replaced the battery (because the battery died while he was waiting for me to drive the 4 hours to get him) and installed a fuel pump relay resistor (from U-Pull-R-Parts). The car ran flawlessly after these two installs. Wondered if it was the resistor or the battery - so, re-installed the old resistor and it still ran fine. Figured the problem was due to the weak battery. I've been driving it ever since (with the original resistor installed) just to prove it out. Well, it has shown up again!

I'll try to get it home and re-install the U-Pull fuel pump relay resistor and see what that does. That is, unless you can provide a better recommendation. Thanks to all in advance!

And even more info:

• I changed the driver's side wheel bearing (installed a Timken) and strut last weekend.
• About 2 years ago, we experienced a similar condition after driving for 6 hours at 70-80 mph - it started to cutout (but would run up to 100mph at WOT). The car died as we pulled off the interstate onto an off-ramp, but restarted and acted just like today. We were able to make our way to a gas station, filled with gas (it still had a few gallons left in the tank (based upon the amount of gas it took to fill it)) and we didn't have an issue during the remaining 4 hour trip home. We followed another post about solving all my Lexus LS issues and changed all the capacitors out on the ECU. The car was running fine before and ran fine after the capacitor replacement - with the problem last Thanksgiving and today, I am ruling out the capacitors as the cause of the initial issue (and the last two issues).

Yamae

Sounds like the insufficient fuel supply to me. I'd simply try bypassing the fuel pump resistor and see what happens. This will increase the fuel pump motor's current. The quickest way to do this is to insert a jumper wire between FP and +B. Be careful for the current going through the jumper wire. It exceeds 10A or so.
https://www.google.com/url?sa=i&url=...AAAAAdAAAAABAE

Losiracer2

are your catalytic converters clogged up? the engine could be struggling to exhaust the gasses if there is a blockage

LeX2K

Check the alternator/charging voltage.

GS4302001

The car didn’t start after work. I tried the jumper but to no avail. Went home and got the U-Pull resistor, installed it, and the car started. As it turns out, that may just have been a coincidence as it died 3 miles into my drive home.

I had it towed home and put it in the garage. I’ll have to check out the fuel pump next week, no time to mess with it now.

GS4302001

Pulled the trim out of the trunk and tested the terminals to the fuel pump --- Open Circuit! Pump on the way from Rock Auto.

Funny how intermittent this thing was as it failed. Well, I "hope" this is the answer to all the issues noted. I'll update later - plan to install the fuel pump and take the car out to my son the next week (12+ hour drive).

GS4302001

No issues since replacing the fuel pump.