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rpm's varies witn cruise on

scooter5

New member
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.
 


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?
 
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.
 
How much variance? Cruise control isn't too much. Usually not enough to make an audible difference.

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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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