Hello, I recently purchased a 2014 GS350 (CPO). One thing I've noticed is the cruise control has about plus/minus 2 miles per hour variance from its set speed as the car progresses over road inclines. This happens in Eco, Normal, and Sport modes.

I know +/- 2 mph doesn't sound like much, but I thought that the car would hold its set speed without much variance. Even with a manual transmission, my previous car (2006 Audi A4) kept its set speed better than the GS.

Anyone else experience the same thing? Was anything done to fix the issue?

 

I have found this to be minor disappointment too, and I notice even wider variations in speed. It seems like the CC is always behind the power curve, so to speak.

 

Yeah all toyotas and lexus vehicles do this. Its like the cruise control is controlled by a wire and is analog by nature instead of Digital speed throttle set. I just get use to it. My 2006 LS430 did this too and its a V8 so its not because of the engine.

 

I never use cruise control...because I don't feel like I'm 'in control' using it...

 

Totally agree, I have had the same issue and with our 2013 Luxury, noticed it right away and have taken it to the dealership questioning why this is happening. This is our 5th Lexus over 10 years and have never experienced this happening on our other ones. Did not get a good explanation on it other than it seemed normally and they were going to look into it..........

It should have no trouble maintaining speed, I don't like setting it at 70 and at a slight incline drops to 68. I intend to check into this further.

If you have checked, post what they said.

 

It's all in the tuning of the speed controller.
Dont know if the tuning can be changed though. My guess is it's tumed to get the best gas milage vs maintaining a very accurate speed.

 

Thats why manufacturers need to know that when we set cruise to 80mph we want it constant at that speed. If we wanted to get the best milage we would be manualy driving the car ourselves.

 

This is annoying on my F Sport also, has been since day one. My old G35 would lock in the speed and the RPMs wouldn't even change going uphill because the low gearing kept it revved kinda high at 75mph to begin with. It got much worse gas mileage due to the lack of a tall 5th gear.

Try this experiment for me (and I will do it too next time I get the chance). Put it in manual shift mode, keep it in 5th gear, then set cruise to 70mph or whatever and hit a somewhat hilly area. See if it's 6th gear (or 8th in newer models) that is causing it to fluctuate.

While I wish it was more aggressive at keeping speed locked when you set it, I don't want it downshifting noticeably for every hill either. Maybe it's a trade off.

 

I've tried to do this before and found the cruise control won't engage in manual mode, unfortunately.

Anyway I agree this is about the tuning of the cruise control, though may not be for economy reasons. I once helped a friend install an aftermarket cruise control that was tunable. You could set it to hold speed very accurately, but it was uncomfortable to ride in that way--it would slam the throttle closed at the top of hills and slam it open again at the bottom. You could set it to be very 'lazy' about holding speed and then it was also very smooth. There was a good middle ground between the two extremes where it would hold speed fairly well but still drive itself fairly smoothly. It would not surprise me if Lexus decided to tune the 4GS cruise control for smoothness instead of tight speed control.

 

Last month I went from Texas to Nevada and back. In the Texas hill country just west of San Antonio on IH10 there are a lot of 6-7% grades. On one stretch near Kerrville( a gorgeous place to retire folks) there is a 3 mile 7.5% downhill stretch that made my cruise downshift like crazy. I had it set to 80MPH and it kept shifting down to hold the speed, when hit 4th gear and the rev's went over 5k, I turned off the cruise. I don't remember my 07 ES ever doing that. Same engine but a different tranny. I just chalked it up to steep grades. On the rest of the trip it held speeds just fine.