I think that's a common problem for many of us.
One trick I use to keep from over-editing is a three-pass rule. I write the rough draft, and then I'm allowed three passes over the completed story or chapter. The first pass is always grueling, and focuses on grammar and syntax. The second pass is for flow and content, and the third pass is to tweak and polish.
After that, I'm done. No more tinkering and over-tweaking. It's posted, and hopefully, it's acceptably error-free. If not, well, someone will be sure to tell me where I screwed up, and I can always fix it.