my for focus 1.8 speedo stoped working but was told it was the speed sensor but my car is reving up to 5k and then doen to 3k and staying there whould the speed sensor couse this problem as well as the speedo not working or whould it be the ivc vales as i disconted this and there no differacnce need help as cars in bits and need the bugger for work

 

Ive just posted in this thread at the bottom, id certainly give it a look, i dont think it would be anything to do with the speed sensor, may be wrong.

The speed sensor is a type of tachometer which reads and monitors speed.