In my opion and perhaps by your local code, placing the intake vent in the garage door would not be a good idea. If the intake vent is in the garage door that would make the air flow path from the door into the room. If someone happened to have an automobile running in the garage to perform a maintenance service this would pull the exhaust gasses from the auto back into the room.

I would prefer to have a fan at the head end of the garage and blowing inward from outside. This would create a slight positive air pressure in the garage and in the event an auto was running the exhaust gasses would flow out through the natural cracks and crevices around the door or throuh an exhaust vent in the door.

Hmm. Good point. Plus, come to think of it my idea would draw car exhaust up into the attic, and as I recall carbon monoxide is heavier than air, meaning it would settle down out of the the attic and into the house through natural cracks and such.

I tend to be pretty conscientious to not run cars in the garage without the garage door wide open, or if the engine has to run for an extended period I'll even back the car into the driveway, so for myself it wouldn't be a problem, but its still one more reason this might not be up to code.

Maybe I could rig a fan to draw air down out of the attic and out the garage. It would have to fight the natural convection but it would still be air flow, and it would be positive pressure in the garage instead of negative pressure. (This is an attached garage, unfortunately.)

Of course, positive pressure in the garage might mean that car exhaust will try to get into the house instead of go outdoors. Dang it, this is a tough problem.

Thanks for your thoughts, it helps me consider new angles.

I too have been researching for some time installing ventilation in my garage.. mostly heat and humidity. I first thought a whole house like fan in garage venting to attic would kill two birds with one stone, but they are apparently against code. RE Williams contractor still shows one on their web page but there is no link. A google search eslewhere showed that the product has been removed from the market because of code.
I will likely install a through the wall fan with exterior louver, perhaps a timer setup to turn on when we drive into the garage.
There are several good reasons for not venting into your attic, or creating positive pressure into your garage from outside: venting to the attic creates a fire chimney from the place where your gasoline products are stored. If the garage were to burn, you just torched the rest of your house

Continued.
You don't want to postitively pressurize the garage relative to the house (fan blowing into garage) because the pressure gradient will accelerate pushing pollutants and heat from garage into your house.

I will likely use this: http://www.rewci.com/121620exfa.html TTW fan to exhaust hot polluted, humid air from garage. If you don't have a through the wall access, a ceiling vent with duct connected through the roof will probably meet code, though you will now have an extra roof penetration.

Here is a link that might be useful: Louvered Exhaust Fan through the wall