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Surging Cruise Control


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Good Morning Everyone,

I have owned my '91 DeVille (4.9 litre) for 7 years and have put about 55,000 miles on the car. Almost daily the car travels 18 miles up and down the Interstate (18 miles one way) with some in town driving. Recently, over the last few years, I have noticed while the cruise control is on the car will surge. Usually this surge unnoticeable and most of the time you don't feel it at all. There are times though where there is a noticeable surge which only lasts a second or less then the throttle immediately backs off. I can place my foot on the accelerator and feel it moving so I know the cruise is telling the car to speed up then back off. When this happens it's usually during a weather change, like a front moving through etc. Now, don't make fun of me yet, I think this part of the problem with the motor adjusting to a new air mixture/density etc. I have been through the 'teach' mode many times on this car to establish the High/Low idle and I know the little servo that controls the throttle stop is very busy. I don't know if this servo is even being used during the cruise or if it's for idle only...but it seems like an electrical issue along these lines.

The reason for the post is recently the surging is getting worse. Just last night, after being on the Interstate for at least 5 miles (motor was at temperature), the car surged 3 times in about 2 minutes hard enough that I could really feel it. Again, back to my weather theory, a warm front did most across Kansas yesterday. :D

Thanks for reading my long post!!

Greg

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It's you. I recommend therapy right away. ;)

But really.... Its the old vacuum operated servo right? You could have a flat spot in it.

Try moving the linkage up so its one hole looser.

I agree on the therapy...might be the best advice I've received yet!! :)

I didn't know it was vacuum operated, I'll take a look at it.

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I think he does have a vacuum operated cruse servo. Look for the usual vacuum leaks everywhere on the engine. Also check the chain from the servo. I THINK too much slack will cause that.

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