Thanks for your reply. I looked through that website, and it seems like good advice. However, I only buy my gasoline from Chevron and Shell (which are listed as "top tier" retailers).

The problem is, my car had the injectors replaced 6k miles ago (about). I can't imagine that gasoline would cause this problem after 6k miles, even if it was unclean gas. But again, I only use Chevron and Shell...

I should also note that I only use high-octane gas, and the previous owner (my sister) has too... I haven't put a drop of low-octane in my car.