01 deville at times engines speeds up speedometer jumps about 10 miles up and down

I am no Honda expert, but a similar problem happened to my ex sister in-laws Ford Taurus. The speed odometer would jump around and it had trouble shifting (automatic transmission). After driving it I changed out the speed odometer sensor on the transmission and it's been fine ever since. I changed out the sensor because if the cars computer cannot tell how fast the car is traveling then fail safes in place go into effect and the computer will do it's best to keep the cars rpm's down based on the speed indicator and not let it shift or shift properly either. If it's getting false speeds then it will shut down the motor when the speed gets to high and allow it to run as the speeds fall (jumping speed odometer needle). It effects the transmission shift points also. It will either shift erratically or not shift out of say 2nd gear, so that the cars engine can't get damaged based on what signal the speed sensor is sending the computer.

Based on your actions, it sounds like a wiring problem.
Could be a weak connection at the cluster, or the speed sensor.

I would look for a broken ground wire..If its a ground wire it should be one of the big ones..Theres one from the firewall to the block..If any body work has been done or major engine work ,,sometimes the grounds are left off..If all looks good it may be in the cluster or the GEM module..

For speedometer related issues,the help links are provided below.Click the link below to go through its details :----

How to trouble shoot speedometer?

http://schematicsdiagram.blogspot.com/2011/06/speedometer-not-working.html

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why speedometer not working? http://technoanswers.blogspot.com/2012/01/1996-fiat-bravo-speedometer-not-working.html

------------ Speedometer works but odometer not working? http://technoanswers.blogspot.in/2012/01/speedometer-works-but-odometer-not.html----------- Speedometer runs backward?

http://technoanswers.blogspot.com/2012/01/speedometer-runs-backward.html

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Warning lights on and speedometer died?

http://howtobyme.blogspot.com/2011/08/warning-lights-on-and-speedometer-died.html

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ABS & Brake lights warning indicator steady on dash and speedometer not working?

http://howtobyme.blogspot.com/2011/11/abs-brake-lights-warning-indicator.html

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Vehicles Cluster panel Not reading Miles?

http://schematicsdiagram.blogspot.com/2011/12/vehicles-cluster-panel-not-reading.html

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Odometer works properly but speedometer works intermittently? http://technoanswers.blogspot.com/2012/01/odometer-works-properly-but-speedometer.html

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How odometer works in cars?

http://technoanswers.blogspot.com/2011/11/how-odometer-works-in-cars.html

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Speedometer not working on Ford?

http://repairhelpcenter.blogspot.in/2012/02/speedometer-not-working-on-1993-ford.html

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This will help.

Thanks

The speed senser is mounted on the transmission. This device is an slocrto magnatic motor and they cost less than $100 there held in with one bolt and have an electrical connector. Many times if it's bad enough the check engine light will come on. This problem but the heating up but work OK cild is a good chance the senser has failed.. The trans mission should be checked for overheating as the senser failure will be heal related

Most likely a speed sensor is going bad (most cars and truck do not use mechanical speedometer cables anymore) most sensors are located near the differential in rwd cars or near the drive shaft on the transmission. Best bet is to get a Haynes manual for your car to help locate the speed sensor. Remove it and take it to the auto parts store so you can visually compare it to the replacement. Install the new speed sensor and it should restore your speedometer and odometer.

Yeah you may need a whole new dashboard because the whole panel circuit for may be messed up.

if both go then its the sensor ,but if car is a 98 then it could be a cable or a speedo cable crive worn out

Yes your speedometer, and odometer are controlled by your speed sensor.

speedometer cable? speed sensor or speedometer meter it's self! engine light on scan obd 2 to retreve codes don't gue$$