I have this Autometer Autogage 5" tach w/ shift light, installed it, wired it good but there's one little problem: the needle is shaking on idle. My idle is fine, around 600-700, but when it is in idle, the needle is shaking. Has anybody experienced this kind of problem? Specifically with this Autogage series? 'Coz before I had a 3" iEquus tach and it never did that, so I was kinda thinking that maybe the tach itself has the problem.

I have a 92 Civic with a stock d15b7, if ever that matters.
Help would be pretty much appreciated.