You will not incur any taint for having unknowingly performed all the kainkaryams to that idol thus far.
There is something called ‘abhuddhipUrvaka utrAgham’ – that is, after bharanyasam, the sins that are committed without being aware. ‘agham’ means sins. As such sins were unintended, no harm will ensue. After having become aware, one must not continue to commit the same sin.