I own a website where students share notes, articles, exams and exercises. Most of this content has bad quality, poor titles and spelling errors, but the website received a lot of traffic back in the days before Panda and Penguins.
Right now, I only allow publishing of articles with "good" quality calculated under certain parameters, but there is a lot of old, bad content still published. I'm removing these old posts slowly, in order to not confuse the Google robot, but this measure is not improving the low rankings. Would it be better if I removed all this bad content at once?