This is not too common to see but I have seen it before. If recent repair has been done I would make sure the grounds are all in tact and tight. Interference can cause the signal to twitch a bit at idle also so make sure the wires are all secured as they should be and sounds like you have already looked over the vss wires. An ohm test on the wires from the vss connector to the pcm connector will verify they are both tact and also check them to ground to make sure one isnt rubbing and causing noise in the signal. Noise on the datastream could cause this also and may be the case since your dash reads zero and hpt shows just above this. Do you have a power inverter hooked up to the car through your laptop when watching this or just using it off of the laptop battery? The dash gets its signal via datastream also so I would suspect noise or interferance between the cable and the laptop especially if your hud shows zero and scanner shows 1-3 at the same time.
