nhester

Using cruise control set at ~40mph there’s a gentle rural hill that my TLX-V6-Tech regularly travels (car in “Normal”). It ascends the hill with very little loss of speed or change in tachometer. However, descending is a tad troubling: the car slowly accelerates (expected) — and suddenly the tachometer surges along with a sudden increase in speed! Of course, I gently apply brakes to bring the TLX back to normal! My previous 2010 TL would never have acted this way…

Anyone else have a similar experience? Is this a problem that can be corrected?

Quandry

There is a downhill slope approaching my home, about a 1km stretch. With ACC set to 60 kph it will slowly creep up to 65+ about 2/3 the way down. I cannot recall any surges but these could be from the tranny rev matching to shift to a lower gear but it should not accelerate. Try it in other modes to see if it does the same thing, but I doubt that there will be any sort of correction.

LaCostaRacer

I'm not sure about the wisdom of engaging cruise control at 40mph- that is hardly highway cruise speed now is it?

I would see what the car actually does before hitting the brakes to know the full story. I know some cruise controls now will allow for a fluctuation in speed to conserve fuel- perhaps that's what's going on but I don't understand the downshift that seems to be happening.

csmeance

the TLX I'm currently driving is a bit aggressive with engine braking when I'm driving downhill with the Cruise Control Set. It's not the smoothest in the world when it does the engine braking to slow down but the speed does not exceed more than 2-3MPH from where I set it.

This is in a 2015 TLX Tech 3.5

Mr Hyde

Sounds like the engine braking, and surge by the engine as it does a rev matched downshift to a lower gear, and higher RPM's. With the TLX so low in the RPM band while driving normally with the 8/9 speeds, the downshifting for engine braking is much more apparent than in other Honda/Acuras.

This is exactly what happens in Sport + mode as well; the car jumps forward a little with each downshift even in the really low gears as I slow for a light, or toll barrier. That is my only complaint with Sport +, but because of it, If the sequential revmatched shifts could be disabled; I would.

lsbuffs

Driving down significant downhills in the Colorado mountains, I was surprised to find the cruise would not hold a set speed. I had cruise at 65 mph down from the Eisenhower Tunnel, yet the car would accelerate far past that, into the 70+ with no sign of engine braking. In my BMW on the same road, the engine braking would hold the speed within a small range around the set speed.

Quandry

The feature on BMW is called Dynamic Cruise Control (DCC), and it maintains the set speed at all times. The TLX has Adaptive Cruise Control but does not incorporate DCC. There might be other cars with ACC that incorporate DCC.

csmeance

if you stay on the gas pedal even 1% the TLX stops engine braking downhill leading to going 5+ MPH. Also the TLX and on most BMW's the braking for CC is done only via engine braking and gear shifts.

Only the ACC equipped cars (both BMW and Acura) get the braking function that enables the car to apply the brakes automatically to slow you down.

holografique

FYI...the behavior from the OP is exactly the same in the 14' PAWS RLX. It will not maintain the set speed when going down a hill. Mine has exceeded the set speed anywhere from 1-7mph+ above the set speed.

I understand the vehicles have ACC, but it is also my understanding that as long as it has not detected a vehicle in front of you, then ACC is not truly active. So why it would behave this way (as long as a car is not in front of you) seems odd to me and not expected behavior.

Quandry

Not sure which model Acura you are referring to, but my TLX does not perform braking function when going downhill with ACC enabled and it not following a car.

rkinmoval

Sorry to bump an old thread but was wondering if anyone else is experiencing significant speed gains while in cruise mode. I have a 2016 TLX without adaptive cruise control and will see gains of 10 miles per hour going down hills with the cruise set at 60 while in Economy mode. This just doesn't seem safe to me. My dealer is stating that is normal and that I should drive in Sport+ mode and then it will only gain 2-3 mph. That kind of defeats the purpose of achieving fuel economy to me. If I put the car in neutral going down the same hill, I gain the same amount of speed at the bottom. Does this seem right? I've never owned a car that will get to +5 mph. I took my 2016 Silverado down the same hill and got to 65 before it seemed like engine braking kicked in. Appreciate anyone's thoughts and thanks in advance.