So I've had my 2015 for 5 weeks now and I've been noticing lately that sometimes when coasting, with my foot off the gas pedal, the car seems to maintain speed 35-40 mph for several seconds before slowing further. I noticed this when approaching a traffic light and the car was taking a long time to decelerate. The car's not cold and is at normal operating temperature. My driving style right now is pretty laid laid back, while I get to know the car. The GS only has 26K miles on the odometer.

Has anyone else noticed this? Is this by design, or maybe a quirk I need to address?

 

I notice this too -- I think it's just a heavy car so the momentum carries

Is what you say true on a slight incline?

 

With many gears, lockup torque converter and a heavy car the idle RPM will keep the car rolling quite a bit. Look at the economy gauge to see if it is high or low? That will give you a clue to whether it is holding the throttle open or just coasting.

 

 

Is this a complaint?

 

I'm not sure...
I expected the car to slow down when there's no input to the gas pedal, but it seems the GS might be maintaining/increasing the engine idle speed to match the vehicle speed, rather than let the drop in rpm and hence engine speed naturally slow the car. If the idle is being artificially increased by the ECU when coasting, wouldn't that increase gas consumption? If that's how the car is designed to perform, then there's no problem or complaint, however if not, I'm seeing if this might be a concern.

In other cars, deceleration is instantly noticeable when getting off the gas, and I'm not talking at high speed, but laid back driving.

 

Not the first time I've read this, tho personally I don't notice much difference between my GS and my infiniti in this regard.

I remember another thread where someone was saying when they set cruise control but then go down a small slope the car increases speed quicker than you'd think. Others commented on how the GS has a pretty low rolling resistance and is actually quite aerodynamic.

 

Are you in sports+ mode because the revs will continue to stay high for a few seconds. The car coasts regularly in ECO/Normal/Sport modes, but not Sports+ mode.

I use cruise control about 90% of my ride every day. You are right, if you have cruise control activated and go down a pretty decent sized down slope, it will pick up speed before braking. So if I am going 40 MPH and hit a down slope, the car will speed up to roughly 45 MPH before it starts to break to get back down to 40MPH. I think it's a built-in speed tolerance by Toyota/Lexus ECU to avoid nuisance breaking and I'm okay with that.

 

No Sports+ mode in my basic GS. I'm in normal mode 100% of the time. Taking it easy until I get to know the GS better.

 

As nice as I can say it, I think you're overthinking the car and it's operation. I'm not a race car driver or a scientist by any means but I don't really notice any more particular glide effect or rise in rpm more than just normal car dynamics. Certainly none that would affect mileage.

It'd be one thing if the car was accelerating out of control.

 

Car makers have designed into their engine management system certain parameters that control when fuel and engine timing is changed, mostly in an effort to increase fuel mileage. Signals are fed by the throttle position, the transmission and the brakes, as well as from speed and temperature sensors. For example (which is purely fictional), the following parameters could be designed into the engine management system: when traveling between x1 speed and x2 speed - if the throttle is closed after having been opened between 2% and 8% for > 6 seconds without applying the brakes or shifting the transmission - the vehicle will be in Coasting mode1 to purposely prevent excessive deceleration for x amount of time. However, if the brakes are engaged during this time the system changes to Coasting mode2 where fuel delivery and engine timing is changed to purposely enhance deceleration.

Different vehicles from different manufacturers over the past decade have had a wide range of small changes made in this regard that mostly go unnoticed. I would consider these habits of your car to be unique to that particular model and year, and working as the manufacturer has designed and intended it to work.

 

Hmm... that is interesting, on my 2013 GS, I don't really have that kind of issue, when I let off the throttle I start to slow down immediately, granted I do have the older 6 speed transmission, so not sure if that is what makes the difference here.

 

Not the first time I've been accused of being over-analytical. I just happen to try to figure out how things work... and why they work a certain way... all the time...
I guess I'm a bit OCD that way... but it could always be worse.

 

That answer certainly peaks my interest, and it does make a ton of sense. My main concern was if my observation may have been an early indicator of a sticking throttle, problematic sensor or some sort of issue. If it was a known issue, I prefer to catch it earlier rather than later.

Thanks for the super-detailed, and purely fictional, response!

 

I have a 2013 GS 350 also and today I experimented a few times at 35-40 mph on a flat road to see what happens when I lift off the throttle and coasted. What happened is - the car maintained the speed that I was traveling at for a number of seconds before it gave any indication of slowing.

Before trying this experiment I honestly could not have told you what would have happened. Does it surprise me? Nope, not in the least. I like it reacting just that way. It is not significantly different from any other automatic transmission vehicles I own or have driven recently.

I did not check what gear it was in at 35-40 mph with slight throttle, but I assume it may have [even] been in 6th gear. If it was in 4th gear, or a lower gear, I would not expect the speed to be maintained as it was.