Made an appointment at the local dealership today. My 2021 continues to hesitate and run roughly when accelerating up hills. It feels like it would feel if I were using regular gas when premium is required or when the air filter or fuel fuel filter needs replaced. My biggest fear is that for some reason the car won't act up when he drives it and I will have wasted a 100 mile round trip. I will ask to also drive the car with him in it.
This otherwise perfect 2.5 year old 350 ES has under 12,000 miles on it. I'm original owner. Acceleration and shifting are perfect all other times except, when going up a hill or grade with gas pedal no more than half way down. Never actually "floored it."
Anyone have any theories of what the problem could be? I'd like to be prepared to screen out any baloney thrown my way.

 

How does it run when not in gear? Does it rev to redline without hesitation in park or neutral?

 

No, nothing at all like any of those things. Quiet, smooth idling, we’ll running engine and car except for hesitation upon acceleration going up hills or grades.

 

There's a few potential causes.
Bad fuel filter or pump (not likely at your mileage)
clogged exhaust (not likely)
Bad air filter (I'm sure you checked it)
faulty camshaft sensor (I would think you'd be getting a code from it which you arent)
Bad spark plug (This is what I'd make them check. I had a Mustang that had 1 bad plug, no codes and only gave me issues in certain situations. It only had 9,000 miles on it too)
Low cylinder compression
Vacuum leak (not likely)

 

Agreed - something is changing when the powertrain is loaded up. Ignition or camshaft-related, and spark plugs are a (relatively) quick check.

The reason I'm asking about revving it in Park or Neutral is to see if it'll hit redline without complaining when not under load.

 

I'll ask them to check the plugs---all 6 of them, in case only one is bad.
Thanks for the checklist. I didn't check the air filter, as I don't know how to! I watched a YouTube on it but I'm afraid I might not be able to put things back together right and I'd create a more serious problem for myself! I'd be surprised if it were the cause, as I rarely drive around any dusty environments, etc. But I certainly will have them check it out. Maybe there's something somehow caught in there. My car is unused in my garage for four months in the winter when we go south. Maybe a little critter somehow got in there?

 

Just managed, with help of YouTube, to access air filter and then put it all back together again. Red air filter appears clean, as I would expect given the car’s driving environment.
Just for what it’s worth, I’m going to buy a tank of premium gas. See if the hesitancy symptom is lessened.

 

I think that has to do something with the eight speed transmission acting funny. Hunting for gears or something.

 

Only uphill? Perhaps the change in gravitational force direction is causing a shifting of something creating a restriction in fuel flow to the engine.

A few suggestions so you can provide a hopefully useful description of the symptom(s) so the dealer's service techs have some good, solid symptom information to work with in diagnosing the issue.

1. How step a hill slope is needed for the symptom(s) to occur? Does the hesitation/rough running vary (and how) with different hill slopes? Is speed a (frequency/severity) factor in the hesitation/rough running symptom.

2. Does the hesitation/rough running occur under cruise control, driver manual control, or both?

3. If you park (out of traffic) on a hesitation/rough running hill slope, does the idling engine have some sort of hesitation/rough running symptom? (If not, you might try to find the steepest slope in your area t see if something really extreme has an effect.)

4. Does the hesitation/rough running show up in the tachometer display? If so, take a short video (or more) to show the service department some concrete evidence of your complaint. (If you can hear a sound effect of the hesitation/rough running include that also.)

5. Look around your dealer's location of features with slopes similar (or greater) than the hill slopes that your experiencing the hesitation/rough running problem. (Hills, freeway on ramps, multilevel parking garage ramps, etc. - somewhere local to the dealer for the service techs to do slope hesitation/rough running diagnostic testing.) Depart early for your dealer service appointment, so you can verify a dealer local slope testing candidate does indeed cause the hesitation/rough running issue.

6. Have a fairly good idea of where and when you've bought gas for your ES. That's mostly so you've thought about it in case questioning about "bad gas" arises.

In brief, the reasoning behind the above suggestions is to develop a good description for the hesitation/rough running issue and the definite conditions under which the issue occurs.

 

Thank you so much for your valuable suggestions. I will act on them.
You must be an automotive profession—- if not, you certainly ought to be!
I’ll keep you in touch.

 

could be especially uphill. I routinely use the paddles to downshift going uphill as the trans heads into higher gear way too soon. But even in the higher gear, I don't feel any hesitation at all and I'm approaching 65k on the clock.

 

Is your car under the recall campaign for the low-pressure fuel pump, if yes just let Lexus to replace the fuel pump

 

Shaboom has a 2021 ES so the low pressure fuel pump recall doesn't apply. That fuel pump issue addressed by the recall only involved 2018-2020 ESs and all subsequent model years were manufactured with fixed fuel pumps.

 

OK captain, thanks. However, won't hurt to just ask Lexus to confirm. Fuel pump is one of the items, though it's not the highest priority, they should check as well based on the symptom the OP described.

 

Thanks. I’ll mention it to them, as it feels the same as If there were an interruption of fuel supply to engine. Never know…