Coolant Temp Sensor
 

Can someone tell me where the Coolant Tempature Sensor is located on a 1991 Civic Hatch std. Is it on the engine or on the radiator. I would like to replace it to see if it fixes an idle problem I am having. Thanks

It's screwed into the head below the distributor. The sensor that drives the ECU is the one with two wires closer to the front (exhaust) side. The one near it with one wire only operates the temperature gauge on the dash.