diff --git a/lib/fog/aws/requests/rds/create_db_instance.rb b/lib/fog/aws/requests/rds/create_db_instance.rb
index 4fe21d287..3c6f64001 100644
--- a/lib/fog/aws/requests/rds/create_db_instance.rb
+++ b/lib/fog/aws/requests/rds/create_db_instance.rb
@@ -73,7 +73,7 @@ module Fog
                  "PreferredMaintenanceWindow"=>"mon:04:30-mon:05:00",
                  "Engine"=> options["Engine"],
                  "EngineVersion"=> options["EngineVersion"] || "5.1.57",
-                 "PendingModifiedValues"=>{},
+                 "PendingModifiedValues"=>{"MasterUserPassword"=>"****"}, # This clears when is available
                  "MultiAZ"=>false,
                  "MasterUsername"=> options["MasterUsername"],
                  "DBInstanceClass"=> options["DBInstanceClass"],
diff --git a/lib/fog/aws/requests/rds/describe_db_instances.rb b/lib/fog/aws/requests/rds/describe_db_instances.rb
index 4b55e8848..7e1f0a63b 100644
--- a/lib/fog/aws/requests/rds/describe_db_instances.rb
+++ b/lib/fog/aws/requests/rds/describe_db_instances.rb
@@ -53,8 +53,15 @@ module Fog
                    server["availability_zone"] = region + 'a'
                    server["Endpoint"] = {"Port"=>3306, 
                                          "Address"=> Fog::AWS::Mock.rds_address(server["DBInstanceIdentifier"],region) }
-                   server["PendingModifiedValues"] = {"MasterUserPassword"=>"****"}
+                   server["PendingModifiedValues"] = {}
                  end
+              when "rebooting"
+                # it applies pending modified values
+                if server["PendingModifiedValues"]
+                  server.merge!(server["PendingModifiedValues"])
+                  server["PendingModifiedValues"] = {}
+                  server["DBInstanceStatus"] = 'available'
+                end
              end 
           end
           
diff --git a/lib/fog/aws/requests/rds/modify_db_instance.rb b/lib/fog/aws/requests/rds/modify_db_instance.rb
index c6e51282e..abfe64467 100644
--- a/lib/fog/aws/requests/rds/modify_db_instance.rb
+++ b/lib/fog/aws/requests/rds/modify_db_instance.rb
@@ -45,7 +45,30 @@ module Fog
       class Mock
 
         def modify_db_instance(db_name, apply_immediately, options={})
-          Fog::Mock.not_implemented
+          response = Excon::Response.new
+          if server = self.data[:servers][db_name]
+            if server["DBInstanceStatus"] != "available"
+              raise Fog::AWS::RDS::NotFound.new("DBInstance #{db_name} not available for modification")
+            else
+              # TODO verify the params options
+              # if apply_immediately is false, all the options go to pending_modified_values and then apply and clear after either 
+              # a reboot or the maintainance window
+              if apply_immediately
+                modified_server = server.merge(options)
+              else
+                modified_server = server["PendingModifiedValues"].merge!(options) # it appends
+              end
+              response.status = 200
+              response.body = {
+                "ResponseMetadata"=>{ "RequestId"=> Fog::AWS::Mock.request_id },
+                "ModifyDBInstanceResult" => { "DBInstance" => modified_server }
+              }
+              response
+              
+            end
+          else
+            raise Fog::AWS::RDS::NotFound.new("DBInstance #{db_name} not found")
+          end
         end
 
       end
diff --git a/lib/fog/aws/requests/rds/reboot_db_instance.rb b/lib/fog/aws/requests/rds/reboot_db_instance.rb
index 7d54b70a8..ef04120bd 100644
--- a/lib/fog/aws/requests/rds/reboot_db_instance.rb
+++ b/lib/fog/aws/requests/rds/reboot_db_instance.rb
@@ -25,7 +25,23 @@ module Fog
       class Mock
 
         def reboot_db_instance(instance_identifier)
-          Fog::Mock.not_implemented
+          response = Excon::Response.new
+          if server = self.data[:servers][instance_identifier]
+            if server["DBInstanceStatus"] != "available"
+              raise Fog::AWS::RDS::NotFound.new("DBInstance #{db_name} not available for rebooting")
+            else
+              server["DBInstanceStatus"] = 'rebooting'
+              response.status = 200
+              response.body = {
+                "ResponseMetadata"=>{ "RequestId"=> Fog::AWS::Mock.request_id },
+                "RebootDBInstanceResult" => { "DBInstance" => server }
+              }
+              response
+              
+            end
+          else
+            raise Fog::AWS::RDS::NotFound.new("DBInstance #{db_name} not found")
+          end
         end
 
       end