1994 Toyota Corolla temp gauge cold

I have a 1994 Corolla, 4 cyl, auto trans, with 153000 miles. I just bought the car which has had very little use for the past 2-3 yrs. The temp gauge stays on cold when the car is moving, but when sitting with the engine at idle for a few minutes the gauge needle moves up to midway between cold and hot. When i start moving again it drops back to cold and stays on cold. When stopped for brief periods, say at a red light, the gauge continues to sit on cold. The car runs well and has heat from the heater. Any suggestions as to what the problem might be? Thanks.