97 sunfire overheats when idling

97 sunfire overheats only when idling. We've replaced the thermostat, took it to a mechanic who replaced a sensor and then hooked it up to the computer diagnostic machine which couldn't find anything wrong with the car. He said it might be an electrical problem. What does that mean, how is it fixed, and how much is it going to cost? Please help.

are you positive your radiator fan is turning on? a good test would be to turn on your air conditioner, if your radiator fan doesnt kick on then, then its most likely your fan motor, or the fuse to the fan motor. i honestly dont know of either of those would trigger the check engine light though

Yes, make sure the fan works. I have an old relay that I have removed the cover and can manually close the contacts to check the fan.
The PCM get a message from the temp sensor, which sends a signal to the fan relay to activate the fan motor.

Did the shop perform a System Pressure check ??? When you say "overhead"....like the radiator boils over...or the temp indicator go into the red ???

JzJzz ..and the man from down under...Cheers :)

also, (for me this was more of a fast highway driving problem, never was a problem while idling or in town) make sure all the air has been bled out of the coolant system