I own a 98 z24 and when i turn on heat sometimes the smell of gas fumes comes out.This just started does anyone have an idea why this is happening?
 
but this only happens sometimes (weird)
 
I would check for a fuel leak.  Like a pin hole size one that comes out in a spray form.  I had a similar problem with collant on a different car.  When i turned on any vents i smelled coolant, turned out to be a really small leak, barely noticable.  Hope that helps.
Shawn M.
PSN ID:  Phatchance249