Need to know the location of the vacuum leak in order to answer this.
Check for vacuum leak
Might be a vacuum leak
I have a leak on my drive shaft left front 2000 cheve Blazer I would like to replace the whole unit
Start with looking for a vacuum leak.
Check the 96 Blazer for any vacuum leaks in the system. A vacuum leak can cause the air flow to only come out of the heat vent.
You failed to mention the model year but a large vacuum leak could do that.
Sounds more like you have a large vacuum leak to me.
Lean condition detected on banks 1 & 2 (left and right sides). Most commonly a dirty mass air flow sensor, or possible vacuum leak.
A vacuum leak could do that, also low fuel pressure or a dirty fuel filter.
Start with a visual, inspect all vacuum lines for problems.
change ur rear differential gasket or ur transfer case is leaking
you may have a vacuum leak somewhere.