So I recently bought my 2017 IS 350 F sport a few months ago and have noticed that when I am coming to a stop at a red light/stop sign, or while I am cruising and let off of the gas, the car seems to downshift pretty hard. Is this normal or am I experiencing a problem with the car? Any help or thoughts would be much appreciated, thank you!

 

Hi MichaelP25,

Congrats on the purchase. Are you in sport/sport+ modes when this happens? Usually, when you are in one of the sport modes, the car will downshift when you hit the brakes suddenly. This is the car anticipating the driver slowing for a turn or maneuver which drops the speed of the vehicle therefore dropping the rpm along with it. By quickly downshifting for you, the car is raising the rpm's and is prepping you for more power and quicker response as soon as you get back on the gas. If you have the car in normal or eco mode, the car will typically stay in gear and allow the rpms to drop along with the vehicle speed. At that point you will notice that when you are gradually back on the gas it feels more sluggish before hitting anywhere near the power band.

 

If you are driving in Manual mode and are coming to a stop depending on the speed the downshifts can be rough or jerky especially going into first. I did a drain and refill of the trans fluid and it helped a noticeable amount

 

Thank you!! I love the car and really enjoy driving it! It is my first ever Lexus that I have purchased so I really am new to the car. I am not in Sport/Sport + mode when this happens, I usually drive in normal since I find it to be better to just cruise in. At first I thought maybe one of my calipers was locking up on me but that wasn’t the case. From what you said, that does make sense on why the car would do that to prepare me to be able to get on the gas after a turn. Maybe I just need to get accustomed to it. Thank you very much for the input and feedback!!

 

I usually just leave the car in automatic since I am driving mostly on busy main roads with lots of cars and traffic most of the time. The only time I go into manual is if I’m on the highway! I will definitely take your advice into consideration and drain and refill the trans fluid! I really appreciate the feedback, thank you!

 

I would suggest looking into the vehicle service history to see if the tranny fluid was replaced. If it was slightly overfilled it could cause this issue.
If there doesn't seem to be any indications it was replaced (drain and fill), then I would suggest getting that done...if nothing else but to confirm the fluid is set to the correct level.
Also the ECU does learn you driving style and adapts to it...given the vehicle is new to you, it's reasonable to assume you don't drive exactly like the previous owner.
The dealer can also reset the learned drive patterns so the vehicle starts fresh with you as the only driver...otherwise the ECU will learn, it will just take a while.

 

I had no idea about resetting the ECU!! I used to have an 06 Acura TL so I’m not really knowledgeable about these newer cars with all the electrical stuff!! The vehicle history shows no trans fluid swap, so I’ll probably just take it to the dealership and have them reset the ECU and see if that makes a difference at all! If not, then I’ll swap the trans fluid since it’s almost at 40k miles and hasn’t been done yet. Thank you for all your help and suggestions, much appreciated!