89 RS 2.8L. what can happen if your cold start valve is not working properly or at all? could it make you car run bad or just on start up? what its functions? how do i know its bad?

In cool weather (like 50* or less) the car will be hard to start. It might take several cranks to get it going. In very cold weather (like below freezing) you may not be able to start it at all. I see you are from California. Depending on where in California you are, you may not notice a thing.