I've noticed this a few times but today it was very obvious. I was on a steep hill in a parking lot, I was in Eco mode (2015 IS 250), I was easing into the gas and the car just jerked forward, not sure if it was in between switching gears but it felt like the car just lost all it's power and came back to life. Has anyone experienced this and why this happens? Last time, I was at the dealer they checked my throttle body and said it was fine.

 

What gear was it in when it jerked? Could it have possibly downshifted while on the hill?

And I have to ask...why would you climb a hill in ECO mode? Seems like the complete opposite of what you'd actually want to do to get up the hill.

 

It must have been in 1-2, the steep hill was a parking lot, ECO mode has the lightest steering

 

I can honestly say I've never heard anyone mention that the steering is lighter in ECO mode.
I know if you had Sport S+ mode, then the steering would be heavier...but you'd have to have a 350 with AVS to get that mode.
It would be kind of ironic that in ECO mode the steering is lighter, because that's actually not ECO friendly lol
Here's why is say that...for the steering to be lighter, it requires more current/voltage from the electrical system to do that.
If it's putting more load on the battery, then that means more load on the alternator, which means more load on the engine...which means more fuel being consumed.
Now the consumption would be so small I doubt anyone would notice...also when driving straight the power assist from the steering is pretty much shut off in any mode...to improve fuel economy.

I'm guessing it's maybe a circular parking structure as to why you need the light steering while going uphill?
Maybe try it in Normal or Sport mode and see what happens.
All that ECO mode really does is delay throttle input/opening...so in Normal mode if you pressed the gas pedal 25%, you get 25% throttle body opening (in reality you actually don't, but for the purpose of this example let's say it's the same).
In ECO mode if you press the gas pedal 25%, you probably get 15% opening at the throttle body...the point being that the ECU just opens the throttle body less based on the same pedal input.

 

No change in steering in ECO mode. I bet the tranny got confused a little climbing the steep hill and didn't know whether to shift or keep it in gear so it shifted but didn't do it optimally. I've had other cars do it on mountain climbs. If it's not a regular occurrence, I wouldn't worry about it.

 

That's what I would think also, but after a quick search I didn't find anything that stated either way, so I can only assume it was a possibility.
Only Sport S+ mode was mentioned.

 

Yeah transmissions get confused at times. Usually you don't notice cause there's not as much demand/load on the car while on level ground. But on a steep grade when you are demanding power, you'll notice it.

 

Normal mode and Eco mode feel the same to me. I, at first, thought Eco mode had lighter steering, but I don't think it makes sense, as Sasnuke mentioned. After driving around some more I decided the lighter steering was in my head. Just use Normal.

 

I am 99% sure that sport mode steering is heavier, I can't find any writing on it but I think I watched a YouTube review on it (which doesn't mean anything), but I can literally tell the difference between Eco / Normal (which have lighter steering) than Sport mode. Sport + mode I know stiffens the suspension of the car. I think the reason why the steering wheel stiffens in sport mode because it makes the car "feel" more responsive, it's heavier so the less you move it, the more the car will move giving you that more 'direct' feeling as opposed to Eco which is lighter which involves you turning the wheel a bit more.

I can't explain it but I can noticeably tell the difference between Eco/Normal and Sport steering heaviness.

Edit: After doing a quick google search, in other Lexus models (GS, IS-F, etc), people talk about differences between normal and sports mode and everyone states that it "tightens" up the steering, I am assuming the same thing happens with the IS as well.

 

You are right. Sport does have tighter steering in F-Sport cars that do not have Sport+. The steering on IS350 F-Sport is the same across ECO/Normal/Sport...only Sport+ has the tighter steering. Also, you indicated in your second post that ECO has the lightest steering. That response made it seem that you were implying that ECO has lighter steering than normal so that is why everyone is posting that ECO and normal feel the same. I think everyone knows that steering typically changes in sport mode (minus the IS350 F-Sport variants).

 

Yes, only Sport mode has heavier steering. It's actually only a really slight difference. In Sport+-equipped cars, I think it's more noticeable, particularly with VGRS.

 

I think we can now clarify that the steering feel in ECO and Normal are the default for the vehicle.
In Sport S+ mode the steering does get Heavier.
So in relation, ECO is lighter when compared to Sport S+, but that lighter feeling is just the norm for the vehicle.
I'm not sure about Sport mode...if it is heavier than the norm or not.

 

Sport mode for those without an IS350 F Sport does in fact make the steering wheel a little heavier. We just don’t have the AVS. Normal and eco mode have the same steering for sure.

 

I completely thought ECO mode does is somewhat converts the car from all time AWD to all time FWD to take advantage of fuel economy. I, however rarely uses ECO mode since I don't like how the engine pulls the car in this mode.

 

If anything, the car is more RWD. It can only send 50% up front when it loses traction. The car powertrain is very old school and simple. ECO only inhibits throttle response. I find no matter what, the IS350 is kinda a gas hog.