1

void Update()
{

		position.x += Input.GetAxis ("Horizontal") * carSpeed * Time.deltaTime;
		position.x = Mathf.Clamp (position.x, -2.3f, 2.3f);
		transform.position = position;

},
2

Basically you want to check if a certain time has passed since the key was pressed, and then execute an action right?

this should do that:

public float MaxTime;
    private float timer;

    private void Update()
    {
        if (Input.GetAxisRaw("Horizontal") != 0)
        {
            if (timer > MaxTime)
            {
                //do the stuff here
            }
            else
            {
                timer += Time.deltaTime;
            }
        }
        else
        {
            timer = 0;
        }
    }

keep in mind that this is just a quick solution and not well optimized. You should look into coroutines for that.