diff -u b/core/includes/update.inc b/core/includes/update.inc
--- b/core/includes/update.inc
+++ b/core/includes/update.inc
@@ -890,9 +890,7 @@
  *   This would migrate the value contained in variable name 'old_variable' into
  *   the data key 'new_config.sub_key' of the configuration object $config_name.
  */
-function update_variables_to_config($config_name, array $variable_map) {
-  // Fetch existing variables.
-  $variables = db_query('SELECT name, value FROM {variable} WHERE name IN (:variables)', array(':variables' => array_keys($variable_map)))->fetchAllKeyed();
+function update_variables_to_config($config_name, array $variable_map = array()) {
 
   // Build the new configuration object.
   // This potentially loads an existing configuration object, in case another
@@ -912,6 +910,14 @@
   // Apply the default values.
   $config->setData($data);
 
+  // Get the default variable map if none provided
+  if (count($variable_map) == 0){
+    $variable_map = drupal_map_assoc(array_keys($config->get()));
+  }
+
+  // Fetch existing variables.
+  $variables = db_query('SELECT name, value FROM {variable} WHERE name IN (:variables)', array(':variables' => array_keys($variable_map)))->fetchAllKeyed();
+
   // Set configuration values according to the provided variable mapping.
   foreach ($variable_map as $variable_name => $config_key) {
     // This function migrates variables regardless of their value, including
diff -u b/core/modules/config/config.test b/core/modules/config/config.test
--- b/core/modules/config/config.test
+++ b/core/modules/config/config.test
@@ -322,7 +322,7 @@
 
   public static function getInfo() {
     return array(
-      'name' => 'update_variables_to_config()',
+      'name' => 'Variable migration',
       'description' => 'Tests migration of variables into configuration objects.',
       'group' => 'Configuration',
     );
@@ -358,4 +358,24 @@
     $this->assertIdentical($config->get('parent.bar'), $this->testContent);
     $this->assertIdentical($config->get('parent.baz'), 'Baz');
+    // Test to ensure varaibles are removed
+    $variables = db_query("SELECT name, value FROM {variable} WHERE name IN ('config_upgrade_bar','config_upgrade_foo')")->fetchAllKeyed();
+    $this->assertFalse($variables);
+
+    db_insert('variable')
+      ->fields(array('name', 'value'))
+      ->values(array('config_upgrade_foo', serialize($this->testContent)))
+      ->values(array('config_upgrade_bar', serialize($this->testContent)))
+      ->execute();
+
+    update_variables_to_config('config_upgrade.test_no_array');
+
+    $config = config('config_upgrade.test_no_array');
+    $this->assertIdentical($config->get('config_upgrade_foo'), $this->testContent);
+    $this->assertIdentical($config->get('config_upgrade_bar'), $this->testContent);
+    $this->assertIdentical($config->get('config_upgrade_baz'), 'Baz');
+    // Test to ensure varaibles are removed
+    $variables = db_query("SELECT name, value FROM {variable} WHERE name IN ('config_upgrade_bar','config_upgrade_foo')")->fetchAllKeyed();
+    $this->assertFalse($variables);
+
   }
 }
diff -u b/core/modules/system/system.install b/core/modules/system/system.install
--- b/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1903,13 +1903,7 @@
  * @ingroup config_upgrade
  */
 function system_update_8009() {
-  update_variables_to_config('system.cron', array(
-    'cron_max_threshold' => 'cron_max_threshold',
-    'cron_safe_threshold' => 'cron_safe_threshold',
-    'cron_threshold_warning' => 'cron_threshold_warning',
-    'cron_threshold_error' => 'cron_threshold_error',
-    'cron_key' => 'cron_key',
-  ));
+  update_variables_to_config('system.cron');
 }
 
 /**
@@ -1918,11 +1912,7 @@
  * @ingroup config_upgrade
  */
 function system_update_8010() {
-  update_variables_to_config('system.rss-publishing', array(
-    'feed_description' => 'feed_description',
-    'feed_default_items' => 'feed_default_items',
-    'feed_item_length' => 'feed_item_length',
-  ));
+  update_variables_to_config('system.rss-publishing');
 }
 
 /**
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/system/tests/modules/config_upgrade/config/config_upgrade.test_no_array.yml
@@ -0,0 +1,3 @@
+config_upgrade_foo: Bar
+config_upgrade_bar: Foo
+config_upgrade_baz: Baz