C# WaitForSeconds not working?

In this game, I'm trying to implement a power-up system. Applying the power-up works fine, but when I try to set a time for it to wear off using WaitForSeconds, it either ignores the statement or acts as a "wall" in the code. However, in other scripts, WaitForSeconds works fine. Any help?
Here is the code:

using UnityEngine;
using System.Collections;

public class Powerup : MonoBehaviour
{

public int effect;
public PlayerController playerController;

void Start()
{
switch (transform.name)
{
case "speeder":
effect = 0;
break;
case "inverter":
effect = 1;
break;
case "passer":
effect = 2;
break;
case "sizer":
effect = 3;
break;
default:
effect = -1;
break;
}
}

void OnTriggerEnter2D(Collider2D other)
{

Destroy(gameObject);

if (other.transform.tag == "Player")
{
StartCoroutine(ApplyEffect(effect, other.gameObject));
}
}

IEnumerator ApplyEffect(int effect, GameObject player)
{
playerController = player.GetComponent<PlayerController>();

switch (effect)
{
case 0:
playerController.horzMoveSpeed *= 2f;
playerController.vertMoveSpeed *= 2f;
yield return new WaitForSeconds(15);
playerController.horzMoveSpeed /= 2f;
playerController.vertMoveSpeed/= 2f;
break;
case 1:
playerController.horzMoveSpeed *= -1;
break;
case 2:
GameObject wall = GameObject.FindWithTag("wall");
Physics2D.IgnoreCollision(player.collider2D, wall.collider2D);
break;
case 3:
playerController.Shrink(.02035f, .01f, 30);
break;
}
}
}

 

Try moving it out of the switch and just using a simple "if" statement after the switch. You seem to only be wanting to wait in effect == 0 anyway.

 

Thanks for the suggestion, but I tried changing the switch to an if and the WaitForSeconds statement stopped everything after it.

 

Could it be, that every condition must have a yield return?