I am currently experiencing issues when using the UmbracoApiController.

Open requests on the IIS

How can I make sure that connections to the API is closed after about 30 seconds?

This is my code for the "GetTransportMethodFromId":

using System.Web;
using System.Collections.Generic;
using System.Linq;
using Umbraco.Web.WebApi;
using Umbraco.Core.Models;
using TransportMethods.Models;
using Umbraco.Web;
using WebApi.OutputCache.Core;
using WebAPI.OutputCache;

namespace TransportMethods.Controllers
{
    public class TransportMethodsController : UmbracoApiController
    {
        string rootId = umbraco.cms.businesslogic.web.Domain.GetRootFromDomain(HttpContext.Current.Request.Url.Host).ToString();

        [CacheOutput(ServerTimeSpan = 86400)]
        public IEnumerable<TransportMethod> GetTransportMethodFromId(int Id)
        {

            HttpContext.Current.Response.ContentType = "application/json";

            UmbracoHelper help = new UmbracoHelper(UmbracoContext);

            return help.TypedContent(Id).GetPropertyValue<IEnumerable<IPublishedContent>>("transportMethods").Select(obj => new TransportMethod()
            {
                TransportName = help.Field(obj, "transportName").ToString(),
                TransportCode = help.Field(obj, "transportCode").ToString()
            });
        }

        [CacheOutput(ServerTimeSpan = 86400)]
        public List<TransportMethod> GetTransportMethodFromIds(string Id)
        {
            var transportnamesList = new List<TransportMethod>();

            HttpContext.Current.Response.ContentType = "application/json";
            string[] transportCodes = Id.Split(',');
            var firstNodeId = Umbraco.TypedContent(rootId).Descendants().Where(x => x.DocumentTypeAlias == "HotellerOgPriser").Where("Visible").Where("getTransportNames").First().Id;

            foreach(var transportCode in transportCodes){
                var transportname = new TransportMethod();

                var tItems = Umbraco.TypedContent(firstNodeId).GetPropertyValue<IEnumerable<IPublishedContent>>("transportMethods").Where(x => x.GetPropertyValue<string>("transportCode") == transportCode);                 
                transportname.TransportCode = transportCode;
                transportname.TransportName = tItems.First().GetPropertyValue<string>("transportName");
                transportnamesList.Add(transportname);
            }

            return transportnamesList;
        }
    }
}