Define the oder? If it's sulfer, you're overheating the cat & probably burning fuel in it.
Oil, gas & coolant smells are self-explainitory.
Condensation in the vent system will cause mold to grow & a stale moldy smell.
The old Lexus/Toyota A/C Expansion valves are pretty bad to stick. That'll cause the A/C to not work, or work poorly, which can also eventually lead to mold growing in there.