Rewrite Query_Var URL Parameter with Slug

Your rewrite rule and query vars filter is wrong. Below is an example based on your query var my_taxoqueryvar

function add_query_vars_filter( $vars ){
    $vars[] = "my_taxoqueryvar";
    return $vars;
}
add_filter( 'query_vars', 'add_query_vars_filter' );

add_action('init', 'myplugin_rewrite_rule' );
function myplugin_rewrite_rule() {
    add_rewrite_rule(
        'results/([a-z]+)/?$',
        'index.php?pagename=results&my_taxoqueryvar=$matches[1]',
        'top'
    );
}