What you have is an auxliiary airslide from a very early V8 either a 380 or possibly even older such as 450 or 3.5 with djet injection.
With this the idle should be high at cold then slow down to normal 500-650 RPM.
Big problems arise when the aircon clicks in because that idle device is "static". the electronic devices speed the engine up as load increases.
You have probably found the idle dropping really low as the car gets warm,you are in drive,air going at the lights and you want to make a turn...right?.
Someone has fitted it because a fault in the electronic device has caused a high idle and they either didn't know how to rectify it or were being cheap.
The heater type airslide such as have will work oK ,as long as remember that it is very limited in it's application.