Is generating intention necessary?

Any intentional action is kamma. We do good and bad actions. Like any other actions, sometimes we do it intentionally, sometimes we just do it without intention. Is it necessary to generating good intention before/when doing wholesome deed? The more we do good deeds the more frequent we create this intention which can easily become an obsession of the mind and create (new) sankhara. But if there is no intention, how can a good action become a good kamma?