Sluggish Acceleration

[u/susowegood1]

I have a 2024 IS350 fsport. It’s my first Lexus so I’m not too familiar with the norms when it comes to this vehicle but recently I’ve been experiencing sluggish acceleration. When I press the pedal, it feels like the car is building to go and then it accelerates. It’s almost like it gets stuck at a speed for a sec or two and then goes. I took it to the dealer awhile back ago but they said everything is fine. Since then, it feels like the delay has increased a bit. It’s weird. Is this common with these cars? I read that it could be due to the throttle sensitivity settings. Someone else mentioned that the car was designed to be driven in higher gears or something to that degree. I’m not sure tbh, I’m not a big car guy but I do recall accidentally hitting the up paddle while driving in automatic awhile ago. I’ve been considering taking it in to my usual mechanic for a second opinion but I wanted to see if this a common thing before spending the money.

[u/Machiavelli_Vendetta]

This is normal for the IS. The transmission is tuned for a luxurious ride rather than all out performance. This means the throttle response is blunted and it favors higher gears for a smooth ride.

If you want the most out of it, you have to drive in Sports mode and switch to manual. (Let the transmission and engine warm up first!)

Then you can dictate what gear you’re in and hit the torque curve correctly for maximum acceleration

[u/susowegood1 → u/Machiavelli_Vendetta]

Good to know! I was concerned at first since my car only has 30k and I just got it a few months ago

[u/Capteverard → u/susowegood1]

Peak torque is 4,800rpm and it redlines at 6,600. So you've gotta put it in manual and rev it out. Also, it has an electronic gas pedal, which causes a slight delay. Pedal commander usually fixes that.

[u/New-Difficulty-9386 → u/Machiavelli_Vendetta]

Technically you can't dictate what gear you're in because it will always shift automatically, you can only tell the transmission what the highest gear you'll allow it to shift to, with the benefit of downshifting and engine braking because of the nature of this.

Of course when high revving, it's effectively the same thing as upshifting like a manual. Also, since it's not a true manual, auto mode will always be faster than manual mode.

[u/Machiavelli_Vendetta → u/New-Difficulty-9386]

Uhh, not sure I’m following what you’re trying to put down.

You read the part about me specifying that you need to be in Sport Mode and in manual, right?

Not sure what year IS you have but mine holds the gear the whole time and will only upshift at redline or, if you execute the shift.

In manual, you can downshift as you please (as long as you’re within the rpm limit) which effectively allows you to dictate what gear you are in and where you’re at in the torque curve. Just like a traditional manual transmission.

[u/Gorgenapper → u/Machiavelli_Vendetta]

Just to clarify things for everyone here (u/New-Difficulty-9386), there is 'D' and 'M' "manual" shifting modes for the IS (2014 - present, not sure about older models).

If you leave the shifter in auto mode and pull the paddles, you will put it into D shift mode (ie. D1, D2 ...) this is where the transmission will only shift up to the number and anywhere in between. If you have it in D4, it will shift between 1st and 4th gear. This mode is basically only good for engine braking while going downhill, and quickly selecting a lower gear or two while driving so you get a quick burst of speed without needing to touch the shifter. For example, if you make a left turn at an intersection and floor the gas pedal but the car doesn't downshift to 1st like you'd expect and only goes to 2nd so it feels like it's sluggish, hit the left paddle to go into D1 which forces it into 1st gear.

The reason for the limited usefulness of D shift mode is because it will revert to auto mode after 3 seconds of sensing your foot on the gas pedal, so you either have to keep hitting the paddles and downshifting / upshifting to reset the timer, or you take your foot off the gas at 2.8 seconds and then put it back on. It's still like a manual mode, but kinda not really.

If you move the shifter to the left, then it goes into M mode (ie. M1, M2, M3). This is more of a true manual mode, it will try to hold the gear as long as possible unless the engine RPM drops or exceeds a certain level. If you're in M4 and come to a stop, it will shift down to M1 for you. Similarly, if you're in M2 and floor it to redline, it will upshift to M3 for you (unless you have fully disabled traction control). It's best used when you're really going for it and have the gas pedal mostly or fully pressed to the floor otherwise the shifts are much slower if you're driving normally or if the RPMs are not high enough.

[u/1trickana]

You sure it's not just taking a moment to downshift?

[u/susowegood1 → u/1trickana]

I think that could be it but I’m not sure.. when it happens, it’s usually between 1 and 2, and then it drops when the car finally accelerates

[u/Surfnazi77]

Are you in eco mode

[u/susowegood1 → u/Surfnazi77]

No

[u/Gorgenapper]

AWD or RWD? I know for my AWD model that there are certain speeds where the transmission knows to downshift for maximum acceleration, if I floor the gas pedal hard.

[u/susowegood1 → u/Gorgenapper]

RWD

[u/Gorgenapper → u/susowegood1]

Are you letting the transmission warm up a bit before going for it? Since it is RWD, I don't know the shift points for when the transmission will know to downshift to the lowest possible gear.

For example, I have a '24 IS350 AWD with the 6 speed auto. 1st gear is good from 0 - 52 km/h.

If I'm driving at 34 km/h or slower and floor the gas pedal, it will downshift to 1st in an instant and take off. At 35 km/h, it goes to 2nd gear and feels very sluggish, unless I pull the left paddle immediately to go into D1, which forces the transmission to drop to 1st gear.

[u/susowegood1 → u/Gorgenapper]

Sometimes but not always. Ok, I see! Thanks for breaking it down for me. It makes sense now! Saved me $100 haha

[u/Gorgenapper → u/susowegood1]

You'll have to test it out yourself, warm up the car and transmission then find an empty road and go at say 15 mph and floor it. If it downshifts to 1st and feels powerful then repeat it at like 18 mph and keep trying until you find the boundary when the difference of 1 mph means it'll either downshift to 1st or 2nd.

Obviously do it safely, and try not to floor it back to back so you don't stress your engine or transmission unnecessarily.

This trial and error process let me figure out that it's 34 kmh (21.something mph) when my AWD model will instantly drop to 1st gear and take off. At 35 kmh (22 mph?) it won't go to 1st, only to 2nd (which I can override with the left paddle, as described above)

[u/EraOF → u/susowegood1]

the transmission and shifts are much more snappy once it’s warmed up. it’s a super noticeable difference. let it warm up first

[u/pewpewtubu → u/Gorgenapper]

Yes, I agree with this. Is350 is heavy and transmission takes time to warm up. Once its warmed, the car should be more responsive.

[u/etch69]

Outside of sport mode the car will be in the highest gear possible when cruising to keep rpm’s low for fuel economy. When you step on the gas, it’s going to downshift into a lower gear. This takes some time.

If you put it in sport mode it will be far more responsive and will stay out of overdrive gears until you get to a speed where they are necessary.

[u/plutom98]

This is normal, ECU requires time to learn your driving habits and adjust the shift points. Try to use sport mode.

[u/gbe28]

Since you bought the car used, you could also try disconnecting the negative battery terminal for about 30 minutes to allow the ECU to do a full reset on the transmission learning algorithm. It might not make a huge difference but it might remove the previous adaptive mapping from the prior owner if they drove very conservatively. Just keep in mind it will also erase your radio presets, clock and seat memory.

[u/NorthYoung8331]

Do you have traction control on? My car was suddenly feeling sluggish and I couldn't figure out why. Then I realized the traction control was on. Once I turned it off, it drives smooth and fast again

[u/Long-Friendship-3046]

I test drove one this past weekend and the car just felt kinda slow when trying to mash it. It was kind of disappointing especially after testing a 440i and an S5.

[u/steak5]

As compared to what car?

Mines feels sluggish too compared some European cars.

[u/z2salman]

This is normal for the IS, mine has that too but it got fixed via RR racing ecu tune ;)

[u/kasualkactus]

It’s slow and naturally aspirated my dude. At least your engine won’t fail like a Q50

[u/vixen-0501]

Not sure if this would be helpful for you but I accidentally overfilled my oil by about 0.5qt and drove like that for a while. During that time I did experience some sluggishness in acceleration.

[u/xMcSwaggx]

There's a reset/relearn procedure that the Lexus/ Toyota can do in tech stream

[u/SinOfOne]

Normal for the car, really.

What you can do is have the transmission and ecu learn your driving habits. Switch over to sport/sport+ mode and drive a bit spirited (reasonably) for a while. It'll start adapting and hold gears for longer, be more sensitive with the throttle, etc. It'll "reset" if you decide to drive normally for some time.

There's also the kickdown. If you really need the power, you can slam the accelerator. There will be the point where pedal travel seems to stop, and then there's the "click" beyond that. It'll drop the car into the lowest gear possible for your rpm range and give you maximum power ans through the upshifts until you ease off the accelerator.

[u/derekprz]

You have to also disable track off to get max torque too

[u/Ok_Blackberry7388]

I would first and foremost move your seat up closer and adjust the steering wheel. You want better command of the acceleration. Also pop it into sport around town and back to drive when on the freeway. Rev those gears. It's meant to Rev high. Enjoy

[u/Wat3rM3L0NB3AR]

I have a 22 IS 350 F Sport, also my first lexus to own but not driven. I've driven a 2015 IS350 as well, they all kinda drive the same - are you in sport mode or regular? regular/normal mode, the acceleration is delayed. In sport mode the acceleration is more responsive. Obviously overtime, the acceleration will dip a bit but not alot.

I feel like it's a maintenance thing like spark plugs maybe? have you gotten the oxygen sensors checked out? When's the last time you had those

Also depends what kind of gas did you put. Did you happen to switch to mid-grade versus hi-octane?

[u/TONEORLANDO]

These cars are kinda weird. You can’t just floor the accelerator from a stop. Theres a sweet spot. The Banks pedal monster also makes a significant difference to throttle behavior, but I also get like 14 mpg with it hooked up