1998 Frontier Tachometer

I don't know if anyone has experienced this or not, the tachometer stays at 3000 rpm all the time on the truck (4 cylinder 5speed ) when running. The motor is not running that hard thats just wear it seems to fail to on an engine start. Is does return to zero with the engine off. Probably a sensor here but not sure where to look................much obliged in advance.