Reactive Extensions Throttle method

I want to Throttle a method call.

This method is called several times (and it writes to a file), so would be nice if it was called after 2 or 3 seconds.

I tried this, but it is calling each time:

Observable
                    .FromAsync(() => configurationRepository.UpdateConfiguration(sessionManager.CurrentTransmission))
                    .Throttle(TimeSpan.FromSeconds(2))
                    .Subscribe();

And the method signature:

public interface ITransmissionConfigurationRepository
    {
        Task UpdateConfiguration(Transmission transmission);
    }

Take a look at WPF FlashMessage
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