Here are some tips on improving your indoor air quality, if you have an attached garage:
1. If located in the garage move your HVAC to the interior of the home.
2. Make sure your garage ventilation vents are working to prevent negative pressure.
3. Remove hazardous storage such as gasoline.
4. Do not run you car or other gas appliances in the garage.
5. Make sure your garage door to the house has a good seal and a self closer.
6. Be sure there are no openings in the firewall.
See the attached video that covers some of these items.