Projectiles shoot in time with Update() function, instead of intended firing rate in coroutine.

I have a script that gets an array of targetables from another script, and shoots at them whenever they are in range. However, it shoots as fast as Update can go, instead of a timed firing rate in the coroutine. what fixes can I do to make it fire at intended firing rate?

 [RequireComponent(typeof(TarGetter))]
 public class ProjectileSpawn : MonoBehaviour
 {
     [SerializeField] TarGetter targetter;
     [SerializeField] float firingRate = 1f;
     [SerializeField] int maxRate = 5;
     [SerializeField] GameObject projectile;
     [SerializeField] Transform spawnPoint;
     private const string FIRING_POINT = "Firing Point";
     Coroutine shootTargets;
 
     public float FiringRate
     {   get { return firingRate; }
         set
         { firingRate = value;
           if(value > maxRate)
             {
                 firingRate = maxRate;
             }
         }
     }
 
     private void Start()
     {
         targetter = GetComponent<TarGetter>();
         spawnPoint = GetComponentInChildren<Transform>().Find(FIRING_POINT);
     }
     private void Update()
     {
         TargetsAcquired();
     }
 
     private void TargetsAcquired()
     {
        
         foreach (Shape t in targetter.target)
         {
             if (t != null)
             {
                 shootTargets = StartCoroutine(FireProjectiles(FiringRate, t));
             }
             else if(!t)
             {
                 if (shootTargets != null)
                 {
                     StopCoroutine(shootTargets);
                 }
                 else
                 {
                     return;
                 }
             }
         }
         
     }
 
     IEnumerator FireProjectiles(float rate, Shape target)
     {
         while (true)
         {
             GameObject fire = Instantiate(projectile, spawnPoint.transform.position, transform.rotation) as GameObject;
             fire.GetComponent<Projectile>().GetTarget(target);
             yield return new WaitForSeconds(rate);
         }
     }
 }