I would look for a vacuum leak.
The idle is computer controlled
A car's steering wheel will vibrate when driving if the car's alignment needs to be adjusted.
Fast idle motor is not working. This is allowing the idle to fall below the threshold of what it should be when the A/C is on.
Possible bad motor mount
Fast idle motor defective.
The problem could be a bad idle air control valve. You could try taking it off and cleaning the internals with carbuerator cleaner. There are so many things that can make a car idle incosistently and stall but I had the same problem in my 2000 mustang and it turned out to be the IAC valve. I eventually had to buy a new one but by cleaning it good i prolonged the life of it by a year.
Bad idle, lack of power. Vehicle may shake or vibrate at idle.
Not sure what your're asking but if it's a question about the location of the Idle Air Control (IAC) valve on a Mustang it's on the front of the throttle body which is on top of the intake manifold. See pictures at Autoclinix.com; select "IAC Replacemnet | Mustang".
The upper engine mount is collapsed. On the passenger side by the coolant reservoir look at the mount If you see 1/4 inch or more gap the mount is collapsed and will cause the whole car to vibrate
I don't think it has one
under the hood!