First, ALL brifters are indexed. The Shimano RX100 (not 1000) group was pretty much a 105 with a different finish and filled the same position as Tiagra does now. They should have be 8-speed indexed in back and either double or triple (there were two models) in front.

If they aren't indexing properly, all you can do is a copious WD-40 flush followed by light oil and hope for the best. Otherwise they will have to be replaced as Shimano brifters aren't servicable.