2D motion help

I have written the following script with the intention of having an object moving back and forth on the Y axis. But instead of moving on only the Y, it is moving on a combination of an X and Y. If you could help, that would be great!

using UnityEngine;
using System.Collections;

public class EnemyMovement : MonoBehaviour {


public float min=2f;
public float max=3f;
public float movement=20;
// Use this for initialization
void Start () {

min=transform.position.x;
max=transform.position.x+movement;

}

// Update is called once per frame
void Update () {


transform.position =new Vector3(Mathf.PingPong(Time.time*2,max-min)+min, transform.position.y, transform.position.z);

}
}

 

Bit confused, you want to move it on the Y axis, but you are changing the x component of the vector?

Also creating a new vector3 every frame is a sure way to force the garbage collector to run. Try:

// at the top of your class;
Vector3 pos;

//in update
pos=tranform.position;
pos.y = Mathf.PingPong(Time.time*2,max-min)+min;
transform.position = pos;

Also, also - is this frame rate independent? Seems like you might need a * Time.deltaTime in there somewhere?