Where is the idle air control valve on 1988 buick century 3.8?

The IAC (Idle Air Control) valve on a 1988 Buick Century 3.8L V6 is located on the throttle body. It's a small, usually cylindrical, electronic component mounted directly to the throttle body. You'll find the throttle body itself on the intake manifold, near the engine's front.

Because there are slight variations depending on the specific configuration of the engine bay, I recommend looking up a diagram or picture of a 1988 Buick Century 3.8L engine bay online. Searching for "1988 Buick Century 3.8L engine diagram" or "1988 Buick Century 3.8L throttle body" on Google Images will give you a visual to help pinpoint the IAC valve's precise location.