Part of the answer to your question depends on the weather where you live and what the problem is with the sealer right now. Additionally, I'm not sure whether you are talking about the sealer on the tile or on the grout. I don't think you'd want to use acid on saltillo and if the floor looks all right, I think I'd just leave it and see how it wears before doing anything about it. If the porch is covered and you don't have a lot of extreme weather, you might not see a problem. In our area, we have too many freezes to use saltillo outdoors. Additionally, I'd suggest that you take the sealer that was used, and a picture of your floor to a place that sells and installs saltillo flooring and ask their suggestions.