YII how to handle custom 404 error page along with other error pages

I want to display 404 error page for that i have made error404.php file in my protected/view/system folder.

By default i have Sitecontroller and it contained error action function as below

public function actionError()
{
    if($error=Yii::app()->errorHandler->error)
    {

        if(Yii::app()->request->isAjaxRequest)
            echo $error['message'];
        else
            $this->render('error', $error);
    }
}

inside main config file it is defined as

    'errorHandler'=>array(
        // use 'site/error' action to display errors
        'errorAction'=>'site/error',
    ),

my problem is i need to customize 404 page only, rest of the error i need to handle the way it is being handle by sitecontroller's error function. But i could not find a way to do that. If suppose i remove 'errorAction'=>'site/error', from the config main then it does show the 404 error by calling

        throw new CHttpException(404, 'Page not found');

but doing that i can only see the page without layout also other custom errors are treated same as 404 while they are not. I read the manual many times but i still cant able to resolve it.