Car idle stall
 

Hey guys,
Latley my '7' has been acting a little strange. It seems to have a slightly eratic idle wich I think may drop a little low sometimes because the car can stall while ideling. It is realy difficult to keep the engine ideling with the air con. on and often this will make the car idle bellow the bottom mark on the tac. (but still above the zero). I don't think that it is the idle setting on the carb since it was changed at a shop only a few months ago. This problem seemed to start when the hot weather came in but I don't know if that was the cause.
Can anyone tell me what is wrong?
Thanks guys, I would love any advice you could give me.

might help,http://pittdp.homestead.com/underhood.html