I made a graph of the problem. Orange is speed and blue is engine RPM. I'm pretty sure that those spikes in the blue RPM readout means that there's something dodgy going on...

Does anyone know what might cause this? Dodgy crankshaft position sensor? dodgy electrics?

I'm a computer programmer by trade, so I'm a bit scared to try and replace any components... Does anyone know how much it might cost to get a new crankshaft position sensor installed?



Thanks!