Bouncing Gauges

When my wife is driving her car the speedometer jumps up and down. You might be going 45 and the speedometer would fall down all the way to 0, then go back up. When you are driving at speeds of around 65 or 70 the speedometer bounces anywhere from 50 to 75 miles and hour. Also, while the speedometer is bouncing, the rpm gauge bounces as well. Most of the time it bounces between 1 and 3 on the gauge. However, recently it has been going up to 4 and won’t come back down. Also, while all the gauges are bouncing, the car tends to jerk or kick real bad. This doesn’t happen all the time, some weeks it goes just fine, while others it does it on a daily basis. I have read about how speedometer cables can make the speedometer go up and down, but I was not sure if this could effect the rpm gauge and make the car kick. Please help, what’s the problem?

How about some details about the car? (make, model, year, …) If it is not very old, then it is unlikely to have a speedometer cable. It is more likely that all the gauges are electronic, and you have a bad electrical connection somewhere.

Sorry, specs would probably been important when diagnosing a car. The car is a 2000 Pontiac Grand Prix and has about 80,000 miles on it. The car had a new transmission in January of 2007.