HOw is the fan speed "slightly off"?

As to the complaint, I don't think it's a vacuum leak. Here is a trick: Let the engine idle, yank off the oil cap. Does the engine vary in speed for a few seconds and struggle to stabilize? If so, there is no vacuum leak. If you can take the cap off and there is NO effect on the idle, you have a BIG vacuum leak because adding the 'leak' of a missing cap had no effect.