Ok Scottydogg, what would cause this? Cruise control Module? 1999 Grand Prix GT. Shut the cruise off and the rpm's stay normal. When cruise is on the rpm,s vary.
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09-09-2016
Ok Scottydogg, what would cause this? Cruise control Module? 1999 Grand Prix GT. Shut the cruise off and the rpm's stay normal. When cruise is on the rpm,s vary.
09-09-2016
no idea. lol
09-09-2016
Scotty you failed me. Thought of you guys as soon as the kid called. Guessing something to do with cruise control module. Anybody else with a thought?
09-09-2016
Cruise control is what it says it is, all it will try to do is maintain a steady speed.
With that comes times when the rpms will fall as it closes the throttle for coasting and then opens it again to maintain the set speed or accelerate to reach that speed again. Often it will even go 1 mph above the set speed and let it fall back to the set speed.
It's much easier to maintain rpm with your foot.
09-09-2016
There is a different torque converter clutch control scheme when in cruise control.
09-10-2016
How much variance? Cruise control isn't too much. Usually not enough to make an audible difference.
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09-10-2016
He said it will vary 600 to 700 rpms with the cruise on. It climbs up and then goes back to normal.
09-10-2016
Sounds like it's downshifting to 3rd then if the rpm jump is that much.
09-17-2016
Ok, Had him downshift it when the rpm's start to vary. It downshifted to 3rd. Is there a clutch pack?
09-17-2016
So its struggling to stay in 4th?
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09-17-2016
This doesn't sound mechanical if everything works great outside of cruise control.
Makes me wonder if the CC box itself is screwy.
09-17-2016
He said it is doing in drive now too.
09-17-2016
Sounds like the 4th gear hub is stripped now.
09-17-2016
Hmm. This sounds like the GTP complaint I had a long time ago. Of course cruise varies TP, thats it's job. To give whatever throttle position keeps it closest to the set speed. Includes downshifting.
I was advised here that the surging I was experiencing might be relative to high humidity. It would start to chug or buck as I would call it, going up gentle hills on cruise while the trans tries to stay locked up and in O/D as long as it can. Tap gas and it downshifts into 3rd. I was also advised here that it sounded like the hub in the trans had gone bad.
My solution was to use only Shell gas and to keep it in 3rd until the speed limit is 50. The cruise can do a better job of holding your speed down when coasting if its in 3rd, and driving in 3rd doesn't hurt anything that I know of. On very humid days, the stock tune just does this or so I was told. By Bill. Its true. Humid days can make you feel this. Good gas lessens the effect by producing a little better power from the same throttle. My trans wasn't bad. It only had a few thousand miles on it. Just relating my experience with a similar complaint, not second guessing anybody
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