erratic rev counter needle

[lescr]

Ive got a problem with my 1.4 redtop sport rev counter needle, on tickover (900rpm) the needle flies backwards and forwards with no set pattern it goes as high as 6000rpm. The engine revs do not alter. to stop it all I have to do is just touch the pedal, increasing the revs by 50 to a 100rpm and all is good. Could this be happening because of a faulty alternator? I can also stop it by changing the ignition coil (old round type) A new one made no difference but an old one off a suzuki jeep stopped the needle from flicking back and forth.

[mattyr]

camshaft sensor maybe

[patmore]

I would say crank sensor or faulty conection on the dials