Cruise Control Going Downhill (std trans)

[ehidle]

I have a 2.0L 5sp 3i Touring. Whenever I have cruise control on and am going down a shallow decline, it seems like the cruise control cannot adjust the throttle finely enough and as a result the car starts bucking pretty badly. Is anyone else experiencing this? The dealer, of course, says it's "normal." BS. They'd tell you flaming squirrels launching out of the tailpipe was "normal."

 

[tsunami]

i have an 04 2.3l 5 spd and the cruise has no problems handling hills up or down... do you have any mods that could be causing issue?

 

[ehidle]

No mods... probably just a defective throttle control or something... I doubt I'll get any help from the dealer since every damn thing is "normal" with this car, from the incessant rattling to the faulty cruise control to the stumbling at idle and the dozens of other little things that drive me nuts about this car...

I'm half tempted to cube it and have it left at the dealership in a prominent place just to let them know what I think of their POS car... heh.

 

[flash75]

I have an automatic 2008.5 Mazda 3, I don't have stumbling but the car will speed up going downhill with the cruise on. My 2002 Protege 5 does not increase speed going downhill. It feels like it applies the brakes. 3 Nissan's I have owned with cruise on would not speed up when going downhill.

I ran a Google search on the subject and speeding up going downhill seems to be a common problem with many vehicles. As usual most dealers say it's normal.

In my 2008.5 owners handbook on page 5-19 is a warning. Quoted in part.
"Do not use cruise contriol under the following conditions:
Hilly terrain
Steep inclines
Heavy or unsteady traffic
Slippery or winding roads
Similar restrictions that require inconsistent speed"
The Protege 5 Doesn't include the first two warnings
"Hilly terrain
Steep inclines"
The other warnings are the same as the Mazda 3 handbook.

A note on page 5-20 reads:
"On a steep grade, the vehicle may momemntarily slow down going up or speed up while going down."

I realize you mentioned the bucking problem but I don't have an answer to that problem. I noticed in your second post you mentioned the engine stumbles at idle, I would think that problem may be the cause of the bucking with cruise control.

Clifton

 

[TheMAN]

http://www.protegefaq.net/tsb/mt000004586.html
http://www.protegefaq.net/tsb/01-008-06.html

 

[larryhan]

I have a 2.0L 5sp 3i Touring. Whenever I have cruise control on and am going down a shallow decline, it seems like the cruise control cannot adjust the throttle finely enough and as a result the car starts bucking pretty badly. Is anyone else experiencing this? The dealer, of course, says it's "normal." BS. They'd tell you flaming squirrels launching out of the tailpipe was "normal."[/QUOTE/)

I agree with Clifton. I have a 2009 Maz 3 Sport 2.0, manual --had the dealer install the Mazda cruise control --works great uphill, and shuts the gas off downhill. Sounds like you have a bit of a lemon. Definitely figure your idle and bucking problems are related. Try a stronger approach with your service manager, or ask to see the owner.

Luck -- Larry

 

[ehidle]

The issue is not speeding up going downhill. The issue is that, as the car does want to go faster, the cruise control bucks the throttle closed.

For example, on a shallow decline, the car starts to speed up, so the cruise control reduces throttle. When the car gains enough speed above the set point, the controller closes the throttle, which finally causes the car to slow down.

Because the cruise controller is closed loop, if the car slows down rapidly, the controller tries to give it a little throttle to slow the deceleration rate. This causes the bucking.

It's just a lousy algorithm. I would bet that all of the 2.0 manuals do this.

 

[TheMAN]

if you stopped bitching and read my post, your s*** would be fixed right now

 

[dnoveau]

08 MZ3 hatch 2.3 manual - mine also surges - I wouln't say it bucks, but you can feel the throttle changing while going down hill as the car speed catches up to the throttle setting. The service bulletin referrred to in the earlier thread does not apply to my car. I kind of like this little quirk in a my quirky car. At least you can feel the machinery doing its job!

 

[ehidle]

if you stopped bitching and read my post, your s*** would be fixed right now

Your post is not applicable to my vehicle. My fault for not mentioning the year of my vehicle. You have my sincerest apologies for wasting your valuable time.

 

[skylar2ups]

Your post is not applicable to my vehicle. My fault for not mentioning the year of my vehicle. You have my sincerest apologies for wasting your valuable time.

Hahaha!

And I have the same problem and I have an automatic... I just coast down hills...