Check the battery. When I bought my rx300 the dealer never checked the battery. (It had 62K miles)... It was giving off a bad odor, Created the headaches, and made the car and me stink really bad. Its the acid that is in the battery that is letting out fumes and traveling in... Almost has a rotting egg smell. They replaced the battery and shampooed the carpets. while the car is off and has been for a while, just remove the battery and see if any liquid is left behind on the battery tray. They cleaned it out the area with a degreaser type cleaner and washed the area to prevent corrosion. (USE GLOVES!!!!... it is ACID!!!) Once you replace the battery, the smell goes away.