What causes the speedometer to jump up while idling or turn up or down the AC?

What is your question?

I thought it might be the AC compressor that is going out because the speedometer jumps up and down while idle or parked, when I turn up or down the AC, if I leave it the AC up while driving the speedometer keeps jumping up from 10-20 mph while at a light or parked and it causes the foot pedal to stick and a fast take off when you tap on the gas pedal to drive?