Hi, I want to build a new deck but I don't remember the name of a card.
It was an artifact that let you sacrifice an instant or sorcery and repeat it all the time you want paying the ability.
Are you talking about Isochron Scepter or Panoptic Mirror? Neither can be used "all the time" but it does allow for at least a once per turn casting of the exiled card. And Scepter is only Instants with a CMC of 2 or less so it seems that Mirror is closer to what you want.
It was an artifact that let you sacrifice an instant or sorcery and repeat it all the time you want paying the ability.