My IROC tach reads several thousand RPM high, but the needle appears to move normally with engine speed. It seems like everytime I disconnect the battery to work on something, when I reconnect and fire it up the tach is reading another 1000 rpm higher. Idle engine speed gives me about 2500 to 3000 rpm and of course at freeway speeds the tach is buried over 7000. Anyone experience this phenomenon? Have a fix? Thanks.