First - this is on a manual transmission Lancer.

All the other gauges on the instrument cluster work fine. But occasionally the speedometer will jump up to 60mph and stay there when driving well under that speed. But it drops down to 0 when I come to a stop.
So at a full stop the speed reads as 0mph. When I start driving at like 15-20mph the speedometer reads 60mph.

If I give a light tap on the top of the dash above the instrument cluster the speedometer needle will normally hop back to the correct speed and go up and down as normal.

Any idea what could be causing this? Does this sound like maybe a speed sensor problem or a failing instrument cluster?

 

If you smacking the dash board fixes the issue I'd say it's a problem with the wiring being loose, or a problem with the cluster, specifically that gauge...my first thought was a faulty sensor, but after reading your post I think you've found the problem already, it's just a matter of isolating it.

 

Yeah, I really don't want to have to buy a new instrument cluster.
Guess I'll take out the cluster and see what I can find.