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Discussion Starter #1
Does anyone else experience rpm fluctuations while on cruise control going up a long slight incline. For example when im doing 50 with cruise set. If im going up a slightly inclined highway...and i mean slight. The car will jump between 2500 and 3k rpm's all the way up the incline. Not only does it drop but it almost sounds like the car just stops accelerating then re accelerates. Almost like its dropping off to shift then just changes its mind. Its also enough of a rpm fluctuation that everyone in the car looks like they are just pimp bobbin to some old school rap music. We look stupid is what im getting at.
 

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Moved to MkIII section for more looks.
 

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ive never had that happen and i use the cruise on the highway all the time. I also have various inclines and declines, but I set the cruise at about 77mph. I suspect that at your speed and with the incline you are at just the shift point where the car doesnt quite know what to do. try either setting your cruise up or down by 5mph and c what happens.
 

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If you have select shift put it into 6th manually and see what the rpm's do. If they change noticeably and the speed remains constant then something's slipping. If somethings slipping that something will almost certainly be the clutches.


Brian
 

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The Car doesn't "Know" its on an incline. All it knows is that that car is slowing down for some reason, therefor its going to raise RPM's and/or downshift to meet the speed you have set. It just happens to be at a sweet spot in this situation, and it going to be more common with a transmission with more gears. Chances are if you up your speed from 50 to 55 it would solve the issue.
 

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The Car doesn't "Know" its on an incline. All it knows is that that car is slowing down for some reason, therefor its going to raise RPM's and/or downshift to meet the speed you have set. It just happens to be at a sweet spot in this situation, and it going to be more common with a transmission with more gears. Chances are if you up your speed from 50 to 55 it would solve the issue.
ok...so a bad choice of words on my part, but didnt i just say that?
 

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Strichmädchen & Koks
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It's not going to raise the RPM on an incline without changing gear. Either it stays at the same RPM or it downshifts...one or the other.

This will be fairly normal at lower speeds in a higher gear. It is what it is.
 

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The Car doesn't "Know" its on an incline.
"Hill start assist" uses the stability control sensors to detect how much of a grade the car is on. I wouldn't be surprised if they feed that information into the cruise control/grade assist programs, given that I've seen more aggressive downshift (or two-gear downshifts) on steeper hills, for the same amount of acceleration above the set point (or application of the brake in grade assist mode).
 

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The Car doesn't "Know" its on an incline. All it knows is that that car is slowing down for some reason, therefor its going to raise RPM's and/or downshift to meet the speed you have set.
That is not the way that cruise control supposed to work.
 

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Maybe not phrased perfectly, but pretty accurate IMHO.

If RPM drops a little during cruise, throttle is opened to compensate. When that isn't going to be appropriate for the speed/rpm a downshift might be initiated.

OP's wondering if a downshift is actually accomplished for a short time, or if it's "almost" doing so before returning to the current gear as well as I can understand the question.

"Hunting" between gears in certain situations has been an automatic trans issue at times since the first 4 spd overdrive types I can remember (80's?). Recommendation to use "D" instead of "OD" was the suggestion then, maybe "hill assist" would answer for similar situations with these where equipped. (or the appropriate alternative for other models)

His original question remains, as to whether others have noticed this with their cars in similar circumstances
 

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The Car doesn't "Know" its on an incline. All it knows is that that car is slowing down for some reason, therefor its going to raise RPM's and/or downshift to meet the speed you have set. It just happens to be at a sweet spot in this situation, and it going to be more common with a transmission with more gears. Chances are if you up your speed from 50 to 55 it would solve the issue.

Most modern cars "know" what the grade is. I drive rental cars 85% of the time and get a new one about every 2 weeks and I can tell you that most of the newer cars appear to know something about the grade.


Brian
 

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Discussion Starter #13
more info

basically what it feels like is this....car is cruising and goes "oh im losing speed, i better speed up" then it goes "whoops i passed the cruise control speed, i better slow down". It does this the whole way up the slight incline. Along with the rpms fluctuating...the speed is not maintained. Its like there is a translation loss between whatever is controlling rpm's and speed. Speed fluctuates by 1 to 2 mph. I expect it to shift if the gear it is in cant maintain the speed i set it to...but instead it just plays little engine that could all the way up the hill. Im glad to know i have one of the rarest quirky operating cars in the world lol :(.
 

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basically what it feels like is this....car is cruising and goes "oh im losing speed, i better speed up" then it goes "whoops i passed the cruise control speed, i better slow down". It does this the whole way up the slight incline. Along with the rpms fluctuating...the speed is not maintained. Its like there is a translation loss between whatever is controlling rpm's and speed. Speed fluctuates by 1 to 2 mph. I expect it to shift if the gear it is in cant maintain the speed i set it to...but instead it just plays little engine that could all the way up the hill. Im glad to know i have one of the rarest quirky operating cars in the world lol :(.
Have you been back to the dealer to have this looked into?

Meagan
 

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when i mentioned it to him, he stated that it was "the transmission warming up".
That is just a silly statement. Gosh does anyone give a shit about anything anymore relating to doing even just a competent job? Its damn near impossible to get good service anywhere. I guess that happens with nothing but overworked, underpaid people in the workforce.
 

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It's not going to raise the RPM on an incline without changing gear. Either it stays at the same RPM or it downshifts...one or the other.

This will be fairly normal at lower speeds in a higher gear. It is what it is.
Depends on how quickly the car loses speed. If it's a major grade that causes a speed to scrub away 5,10,15 mph. Throttle opens up so far then the kick down will activate. If its a minor grade 3-5mph, throttle will open up but it will reach the targeted speed without needing that kick down to avoid stalling.
 
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