[lkchris]

Any gasoline engine requires a bit richer mixture to run when first started cold. Along with this it requires a little more throttle than is normal for warm idle.

A vacuum leak will undo this.

But, most cars of this era feature something called the idle control valve, whose purpose is to bypass some air around the maf to create extra idle speed. Mixture is richened electronically based on a temperature sensor.

So ...
Vacuum leak
Idle control valve
Temperature sensor

Fwiw but not applicable here, the advent of direct gasoline injection may eliminate the need for these components. Problem is mixture adhering to cold intake manifold and not making it to combustion chamber ... that's why engines require "choke." Mixture obviously doesn't pass through intake manifold with direct injection. "Intake manifold" describes anything behind the intake valve ... including spraying on to it from the back side.