'99 vs statesman, tacho jumping round on decelaration

[pjdm1980]

My '99 Supercharged VS Statesman's tacho jumps round from 1000 rpm to 1800 rpm when i go down hills at speeds of 80 kph and over is it normal or
what do you think is causing it because it doesn't surge like it the engine is actullaly reving but the tacho still moves.
And a second question, the temp gauge never moves over 1/4 mark and usually sits just above the cold mark is this going to hurt the engine or should it be ok, i think it might have something to do with my climate control always feels cold than the read out on the display?
Thanks for any help you can give!!!!

[pjdm1980]

Anybody got any ideas?

[OzJD]

Check the rear of the cluster for dry joints.

[hako]

My guess which may be way out is the the TCC (torque Converter Clutch) is locking/unlocking for some strange reason on over-run. I think on over-run or going down hill it should unlock and then stay unlocked till a steady speed above 80kph is achieved on a constant throttle setting. The fact that it only happens around 80kph kind of indicates that it is transmission related as this is the speed that the TCC comes into play.
Do a codes check - maybe there is a transmission fault logged there.
Checking error codes VR/VS (Revised)
Good Luck.