I just installed an IAC valve in my '92 Tracer, which fixed the poor
> idle and stalling problem.
>
> Now, a couple of days later, the engine has begun racing at times, for
> no reason. It eventually adjusts itself.
>
> What do I do to fix this problem?
disconnect the battery for 15 minutes and reconnect. That should reset the ECM and hopefully that's all it needs.
-Bruce