Maybe a totally differant situation, but... In my wifes 01 Heep Cheroke I started to smell a real foul smell from the engine compartment when she would park it after work. I thought she may have hit something so I looked under it. Nothing. A week later she got a dead battery. I was taking out the old one and the battery had boiled over because she leaves her cell phone charger pluged in all of the time causing a constant low draw. The batt acid leaked on some of the wires and the fiberglass/ plastic batt tray causing the smell. New tray, battery and wires. No more foul smell. Battery acid will make you nausiated(sp?).
Good luck!