i have a 91 da b18a1 completely rebuilt to stock specs. the car warms up and idles fine but after driving for about 10 minutes the temp gauge will shoot all the way hot and stick there. if i tap the dash above the gauge it drops back down to normal temp. i switched all the gauges out of my 92 da and they worked fine in that car. at the same time as this happens with the temp gauge my motor will idle up 100-200 rpm and then drop back down no matter what rpm the motor is at. i dont get a check engine light or any codes off the ecu. i would rather not take it to the shop im sure its an easy fix i just can figure out what could be wrong.