Recently my car has been overheating when idling at a standstill. The fans aren't coming on reliably, although they did come on when I turned the car off. I tried unplugging the connector from the switch on the thermostat, but they stayed on. Then I unplugged the connector from the coolant temp sending unit (the one under the distributor), and the fans then turned off. They came back on when I plugged that back in, but then turned off again as soon as I started the car up. What is the most likely culprit? The relay, fan switch, or the temperature sender?