If you're only getting a code on cold starts, and everything else is normal, that narrows down what could be going on a bit.

On my 91 there is an additional air valve each side of the engine. When the engine is cold its function is to send additional air to the engine to help adjust the idle.

If one of these was bad, that would likely throw a code that would disappear once the engine started to warm.

Maybe someone else will have some other ideas for you