do vacuum leaks cause high or low idle condition?

 

I suppose either, but vacuum leaks I've tracked down are 90%+ low idle.

 

If your vehicle uses a MAP sensor a vaccuum leak will raise the idle .
If your vehicle uses a carburetor, AFM or MAF sensor a vaccuum leak will lower the idle.
AFM sensored vehicles [22RE and 3VZE have it] are especially sensitive to vaccuum leaks.