The cold start valve is the little torpedo-shaped unit directly under the throttle body (in the "U-turn" of the manifold).
When cold, the "gate" is open, you should be able to see through it. It closes the gate by applying 12V to a bi-metal strip.
The ECU temp sensor usually causes problems because, when it poops itself, it tells the ECU that the engine is still cold, and you run extremely rich.