tacho glitch

[pug306driver]

For some time, now and again, whilst driving, I have had cause to look at the tacho, as now and again out of the corner of my eye I seem to have seen ( or think I have )  the tacho "glitch", but on looking at the tacho, all seems normal. Its as if the tacho suddenly stopped working, making me look at it, only to find all is well ?

Anyways, reconnected the battery yesterday and all was normal, even the door locks for a minute, but  now and again the tacho seems to have a glitch and momentarily stop working, with the needle dropping about 200 revs from 2000, only for the tacho to start working again and the needle return to 2000rpm, all in the matter of a second. There is no dip in engine speed or noise or revs or any misfire, just the tacho needle drop and then return ??

Please can someone tell me what drives the tacho, the flywheel "rev counter" or the cam "rev counter" sensor ??

I did notice the quite quiet high pitched whistle/whine noise  again, maybe linked ??

[FuST]

The tacho is driven by the flywheel sensor (crankshaft position sensor). It feeds it's data to the ECU, which in turn sends a signal to the tacho.
Since there's no drop in engine RPM I'd rule that out (reading/recording live data with PP2000 or a ELM327 would prove it for sure).
I'm guessing it's either a bad connection on the back of your instrument cluster, might also be a ground fault of some sort.

[Poodle]

This is usually down to an earth problem.

[pug306driver]

Could well be an earth problem, probably related to the water ingress problem and lock/unlock/immobiliser problem that happens when it rains, next job is drivers seat out and door pillar plastic to get access to the electronics unit down there somewhere.......