I have a 93' escort GT and the voltage regulator is actually part of the alternator (all one piece). I had to replace the whole thing. But if yours is a 2 piece, it would be bolted on the outside of the alernator.
Parts from Ford Escort/ Mercury Lynx, 1981 thru 1990 cars should fit your car. If you get your car parts from a salvage yard, please be sure to check the engine size of the car that you are removing the parts from.
The idle air control valve on a 1990 Ford Escort is located on the intake manifold. An idle air control valves function is to control the amount of air that is allowed to enter the engine so the idle can stabilize.