Need to put car on a scanner that does real time sensor data. One of the readings you can view will be what speed the pcm is seeing from the vss. If the reading on the scanner fluctuates like your speedo, then theres a problem with the vss, it's wiring to the pcm, or the pcm. If the reading the scanner gives is correct and the speedo is off then the problem lies in the speedo itself, or the wiring from pcm to speedo.
Common problem with electronic speedometers is the circuit board inside going bad. One of the first symptoms, many times is a needle that jumps around.
Common problem with electronic speedometers is the circuit board inside going bad. One of the first symptoms, many times is a needle that jumps around.