houston_fd

I just got my first fd this past weekend. decided i'm going to do a light tune up. Started with my oil change. Per the board suggestion, I live in Houston so I put 20-50 in the car. It was driving fine yesterday during the day, but at night I was noticing that the rpm's were bouncing when I idle at a light. In addition, the oil pressure gauge was bouncing too. When I would accelerate, the oil pressure gauge would rise to almost 100. What could be causing this problem? Any help would be greatly appreciated.