I believe that I know what the problem is. I have a 1999 Frontier that was having the same problem. I took the instrument cluster out and found that there is a ribbon cable at the top of the cluster bewteen the two larger gauges that was not connected all the way. It appeared to be but once I loosened the retaining clip(that holds ribbon cable in place), pulled the ribbon cable out, and re-seated the ribbon cable, I could tell the cable was not completed inserted into the recepticle. After reconnecting the cable and reassembling the dash, I haven't had a problem since. Hope this helps. Also, if you have access to electrical contact cleaner, you may want to hit the receptical and the ribbon cable with it and let it dry for a minute or two before you reassemble the connection.