The problem is the cooling fan is not coming on at the correct time. It over heats at idle only. On the freeway it is fine. The fan only comes on when it is to late and it starts to overheat. I replaced both heat sensors the one for the ECM and the one for the temp. gauge. When I turn on the heater on and set at any heat range it turns the fan on manually and the car does not overheat. So I think the problem is the ECM computer has a glich in it.
Most Camaros operate with a very high temp. Mine is 1989, a little older then yours but still thesame problem. I replaced my temp unit with one from Jet products. This one comes on at 180, over heating was gone.
there is a sending unit under the plastic on the passenger side on the radiator, it is the sending unit to tell the fan when to come on, on a stock 5.7l Camaro after 1993 the sending temp was 190-195(f) to kick the fan on, this in my opinion is way to hot. dont think that just putting in a lower temp thermostat will solve the problem either, the OBD2 system that drives your computer will think the car is never coming up to temperature (195F) and run the car more rich , you can lower the thermostat to 160(f) by installing the bridgable computer link (also give you the power chip) and it will run faster and cooler,
but for a short shot at cooling, go to your local Chevy dealer and get a lower temperature sending unit, some are adjustable, I have seen them At Pep Boys / Advanced Auto / AutoZone Etc.. they are about 35-50 bux.
A 94 is not OBDII. That started in 96. Some of the fans don't come on until 219 degrees. If the fan comes on with the defrost or A/C that usually means that the computer and relays and circuity are ok. The fans aren't needed when the speed reaches 40 mph as there is enough air flow over the rad at that speed. Take your car to a shop that you trust(ask family or friends) and have them hook your car up to a scan tool to see what temp the fan comes on at and then you will know if it is really running hot. HTH