smoke/foul odor entering car's cabin even when a/c recirculating is closed

Mantrade just replaced my whole aircon system but lately i noticed a smoke/gas fume from the car ahead of us entering the
car's cabin. Will covering the two open holes just below the windshield/ along wiper assembly area be a quick fix? Is it safe for the
passenger inside and the car? Will it have any effect in the quality of air inisde the cabin? Any help please?