I just had my car looked at not to long ago, and the guy mentioned my car is running a bit rich, and the engine does not have the correct VAC. He said it wasnt to low though. I didnt even think of asking him, but could vacuum leaks cause this, or is there anything to consider??
in my experience, a vac leak (esp unmetered vac) caused a tendancy toward leanness, not richness.
a stockish motor should pull 15-20 inches at idle. you can grab vac at the vac tree and check yourself (remember things like aggresive cams can affect vac).
otherwise, inspect lines and gaskets. i have found that the lines in the front of the upper intake (but below it) get cooked.
good luck.
Big cams, and leaks can cause low vaccume. Blocked exaust can also cause low vaccume because gasses not able to escape will back up and when the intake opens there is pressure there instead a vaccume. Bad compression also can have an effect on vaccume.