$("#yourselector").autocomplete({
            source: "your URL",
            minLength: 2,
            select: function(event, ui) {
                $('#selector').val(ui.item.YourDataResponse);
                $('#selector').val(ui.item.YourDataResponse);
            }
});

// Destroy the combobox
$(".combobox").combobox("destroy");

// Unselect the currently selected option
$("#selectlist option:selected").removeAttr("selected");

// Select the option you want to select
$("#selectlist option[value='test']").attr("selected", "selected");

// Create the combobox again
$(".combobox").combobox();