Temperature Gauge

I have a 97 Sunfire 2.2 automatic. The temp gauge doesn't rise. Scanner says high temp fault. After I clear the code and restart the car the gauge comes on after a minute. Then after another minute it turns off and the engine fan comes on and the same code comes up. I have replaced the sensor, and re-terminated the connector. All of the grounds are clean, with less than an ohm to ground. Car is also idling rough, sometimes stalling. Outside of changing the ECM, any ideas?