Aack! Buy a new set of wheels!!! But RoPo, are you sure it's a rodent? Have you gotten down and looked up into the undercarriage of the vehicle?
Funny aka sad story, depending on who you are (and why I suggest check the undercarriage of the car)... when I was a little kid, we had a rambler station wagon. Mom loaded us kids up in the car for the dentist visit. It was a long drive into the city to the dentist. We get there, and it was smelling like someone burnt chicken dinner. Went inside, got our dentist appointments taken care of, and came back out to leave a couple hours later. The car wouldn't start, it still smelled like burnt chicken dinner but a little, ok a lot, worse. Looked under the car too see our nasty old rooster's legs dangling down out of the engine compartment. He took his last ride, must've roosted up there overnight, and that was his final resting place (until he was pried loose by dad hours later). Mom was mortified because we were still there waiting for dad to come rescue us and the dentist office closed, and out came the dentist and all of us kids announced that mom killed the rooster and it was stuffed up in the car and oh look, there's his legs! Mom could have killed the three of us, she was so thoroughly embarrassed. Well think how that rooster felt! I think I was about 8 yrs old then. Now my first instinct is I always check underneath when something suspicious smells fishy, or chickeny, or rodenty.
If it were me, I'd check the undercarriage first, then if you still narrow the smell down to the carpet in the passenger side, I'd pull the carpet up. That smell has GOT to be lingering in your clothing when you exit the vehicle...