To locate it definitively, you'll need to:
1. Consult your owner's manual: This is the best resource as it will have diagrams and specifics for your exact vehicle.
2. Look at a repair manual specific to your 1999 Buick LeSabre: These manuals have detailed diagrams and instructions. Chilton and Haynes are popular brands.
3. Search online for images: Search for "1999 Buick LeSabre [your engine size] PCV valve location" on Google Images. This can help visualize where it's generally located.
The PCV valve is usually a small, plastic valve with a hose connected to it. It often looks like a small, capped cylinder. Remember to be careful when working near hot engine components.