Retain the gasket. Many new IACd's don't come with a new gasket.
There are two style IAC's. It relates to the pintle shaft. One is smooth round and the other has 2 grooves running the length of it. Adjustment procedure is different for each, but both should have an initial adjusted length from the tip to the gasket flange of 1 1/8 inch.
To adjust the smooth shaft valve, hold the body in the palm of your cupped hand. Using the fingers of that hand, pull the spring out of the notches in the pintle and screw the pintle toward the valve body until you have the correct length. Be sure to locate the spring back into th notches on the back of the pintle head.
To adjust the grooved shaft valve, hold the body in one hand and using your fingers of the other hand, press on the tip of the pintle and rock it side to side. It will slowly move into the valve body until you have the desired length.
If you go a little too far, don't worry. It will adjust itself. A problem and damage can occur is when you don't retract it far enough into the valve body.