Under the manage search engines section in preferences, I deleted the original Google search engine and added a new one with the same "URL" string. When I type in the Omnibar, search works fine however it fails to autocomplete the word. How should I remedy this?
As far as I know, there's no way to manually re-add the default Google search with all its features.1
However, you can delete the configuration file that contains user-defined searches and let Chrome recreate it.
1 The default Google search doesn't appear in the Web Data like user-defined searches. Selecting the default search modifies the properties