it could also be the tacho magnet, this is at the far end of the belt armature of the motor. there is a cap with two yellow wires, take it off and check if the little round magnet is
a-------in its position, ie screwed in tight and
b-------not damaged!
also there should be no damage to the wires, these lead to the on-board computer...
regards
gg smit
south africa
gg smit, May 2006