AI wandering script needs help.

Working on this script that have the enemies wandering around after spawning, then found out they wander really far off into the distance, found a script that makes them head back towards the spawn point after some time went pass, the AI rushes back to the spawn nodes and just crowding the nodes. I'm new to scripting and can't seems to find where to implement the codes to make them go back to wandering again. Also I'm working on AI follow and attack script within this script, can anyone point me to a tutorial that can help me implement the codes to this script I'm working on.

 var speed : float;
 var isWalking : boolean = true;
 
 var target : Transform;
 var centerEnemy : boolean;
 
 
 function Start () {
     
     target = GameObject.FindGameObjectWithTag("SpawnNode").transform;
     randomRotation ();
     test ();
 }
 
 function Update () {
     
     if(centerEnemy) {
         transform.LookAt(target);
         transform.eulerAngles = new Vector3(0,transform.eulerAngles.y,0);
     
     this.transform.Translate(Vector3.forward * speed);
     }
 
 }
 
 function FixedUpdate () {
 
     rigidbody.AddForce (Vector3.down * 500);
 
 }
     
 function randomRotation () {
     
     while(isWalking){
     
         yield WaitForSeconds(Random.Range(5,10));
         transform.eulerAngles = Vector3(0, Random.Range(0, 360), 0);
     } 
 }
 
 function test () {
 
     yield WaitForSeconds(10);
     centerEnemy = true;
 
 }