Translation:He often came to have a discussion on Sundays.
The use of the Imperfect "venait" also indicates a habitual action in the past (one of 5-6 different applications of the Imperfect tense). Discuter can be used intransitively, too, meaning simply "to talk" or "to have a discussion". Discuter le coup is a familiar expression for "to have a chat". http://www.larousse.com/en/dictionaries/french-english/discuter/25766
Because of that, this sentence would be well rendered as "He would often come to talk (-or- have a discussion) on Sundays". It is one of the classic uses of the Imperfect tense in French.
[Edit: a downvote with no explanation? Do you not like my after-shave or something?]
Working on my french during the stay-at-home order, George. Let me take this opportunity to thank you for all I have learned from you on Duolingo these past few years. Your moderator posts are unfailingly educational, interesting, and charming! Thank you and stay healthy!
As I said, to avoid any ambiguity between time of discussion and topic of discussion, we would use "à propos de" if the topic is also about time.
Note that "discuter quelque chose" often means "negotiate something" (conditions/price) or even "question something" (decisions).
"If you use the construction LE + DAY it means something that you do every week on that day. Le lundi, je dîne toujours au restaurant. (every Monday)." More here: http://www.frenchtoday.com/blog/how-to-say-the-date-in-french-le-or-no-le
Ok, this time i tried "he often came for discussions on Sundays", and got marked wrong for using "discussions" plural instead of singular - which i think is harsh. One can't translate "discuter" directly as "to discuss", because in English " to discuss" has to have an object, and since this person often came "to discuss" "on Sundays", surely there were several discussions?