My boyfriend and I are thinking about buying this 2003 Ford Focus zx5. Apparently the speedometer sometimes works...but then occasionally it will slowly just start rising...stick about 80 (even when you are going about 20) and then when you go to stop, it just falls to 140 (max) and just doesn't do anything. I know NOTHING about cars... and just want to know if this is an easy fix, or if it is enough to suggest not buying the car...thanks!