I had a similar issue with a Drupal autocomplete field I had created, where I wanted the form submitted when an item from the dropdown was selected.
This blog post addressed the issue for me: http://othermachines.com/blog/smart-autocomplete-navigation-drupal-7
The relevant JQuery code you'll want to look at on that page is this:
(function ($) {
Drupal.behaviors.programmeSearch = {
attach: function (context) {
$('#edit-autocomplete-field').focus(
function(){
$(this).val('');
});
$("#edit-autocomplete-field", context).bind('autocompleteSelect', function(event, node) {
var key = $(node).data('autocompleteValue');
var label = $(node).text();
// If matches found...
if (key != '0') {
// Set the value of this field.
$(this).val(label);
// Redirect user to entity path.
window.location = Drupal.settings.basePath + key;
}
else {
// If no matches, reset.
$(this).val('');
$(this).focus();
}
});
}
};
})(jQuery);
You probably won't need all of that code. Whatever you want to happen on the select event, put in the condition beginning with
if (key != '0') {