He influenced early Protestant thinkers, yes. If Protestants made sure they read St. Augustine without their own 16-century cultural baggage, without Calvinist desacralizing attitude, and in harmony with other Church Fathers, they probably either would have remained in the Church, just like St. Augustine remains our authority, or they would have veered into heresy similar to Jansenism, and would have recoiled from it in the fullness of time.
Several people already explained how Catholicism understands St. Augistin's teaching on Grace.
If there is a thread now or later dedicated to the issue of irresistible grace, I'd be happy to participate. This thread is dedicated to confession of sins. Discussing a more fundamental protestant errors that lead the Protestant into refusal to recognize yet another sacrament of the Church would be like discussing whether America exists on a thread dedicated to American economy.
Oh yes, at first Augustine was a terrible SINNER..but by the prayers and tears of his pious Mother, Monica,he was brought to the relization of the AWFULNESS OF SIN..repentened and became a Bishop and SAINT in the Catholic Church.