Jeff Grant

Hi Guys, I have just acquired a v4 Sti RA, it has had a early Possumlink ecu in it for some time and has been tuned well on this. My biggest problem with this is the tachometer. The car has a factory dash, the tachometer works fine and smooth when not on accelerating, once on boost or with any throttle the tacho needle bounces around. I have tried searching and found other people with the same thing, but no solutions mentioned in the forum. Anyone have any ideas what it is, and what could fix this? Thanks JeffÂ