intermittent tach probs
 

hi all, this happened to me twice in the last month. when cruising on the highway, i notice that my tach is way wayy off. for example, when traveling at 60 mph, the rpms are about 2.5 - 2.7k but then one day it said i was at 4k rpm. so i pull over and see where i would idle at. and i would idle really steadily at 800 rpm. well under 1k lets just say. so it seems like it gets inaccurate at higher rpm. idk, well any of you guys have any experience with this?