ASP .NET Web API route not found

I have a pretty basic ASP.Net Web API project with an ApiController class as follows (greatly simplified here, as the issue is the routing, not the action of the methods):

// A Controller for accessing data from ord.WarehouseFreight
[RoutePrefix("api/ordWarehouseFreight")]
public partial class ordWarehouseFreightController : ApiController
{
    // Get all values from ord.WarehouseFreight
    [Route("")]
    public IHttpActionResult Get()
    {
        List<ordWarehouseFreight> output = new List<ordWarehouseFreight>();
        return Ok(output);
    }

    // Return a single value from ord.WarehouseFreight using the primary key as ID.
    // <param name="id">The WarehouseFreight Primary Key.</param>
    [Route("{id:int}")]
    public IHttpActionResult Get(int id)
    {
        item = new ordWarehouseFreight();
        return Ok(item);
    }

    // Get selected values from the ord.WarehouseFreight
    // <param name="idList">A comma delimited list of ord.WarehouseFreight Primary Keys.</param>
    [Route("{idList}")]
    public IHttpActionResult Get(string idList)
    {
        List<ordWarehouseFreight> output = new List<ordWarehouseFreight>();
        return Ok(output);
    }
}

The relevant portion of the WebApiConfig.cs class (the Register method)is:

        // Web API routes
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );

So far, so good. I can access the API methods using GET and a REST style Uri, such as:

localhost:51953/api/ordWarehouseFreight

to hit the 'Get()' method,

localhost:51953/api/ordWarehouseFreight/2716253

to hit the 'Get(int id)' method, and if I use

localhost:51953/api/ordWarehouseFreight/3928374,2716253

it actually hits the third one, 'Get(string idList)' (which, note, returns a LIST of records, not a single record like the 'Get(int id)' does).

Problem is, in some cases I want to get a list that may consist of only a single item (but is returned as a list, which is handled by my Angular 4 front end as a list of JSON objects). If I only pass in a single record id, I get a single item, not a list.

So, what I want to do is pass in Request params (not pure REST, I get that), like this:

localhost:51953/api/ordWarehouseFreight?idList=3928374,2716253

or

localhost:51953/api/ordWarehouseFreight?idList=3928374

and return a list in either case. However, when I use those URI's, the first Get method (with no parameters) is matched.

Finally to the question: what must I do to get the Web API to match up with the third option? From all I've read so far, here on SO and elsewhere, I'm doing all that's needed. Obviously not.