It started about 3 weeks ago. It smelllllls so bad. I've learned to cope but we still have it.
Seems to be coming out of the air system cause for example, if I turn on the airconditioner it comes even harder.

Or just running the engine and driving, makes it worse than if cold and not on.

I've heard some people say that it might take 5 weeks or soething for the rat remainings to burn out. But then I heard that the smell may remain forever in the upholstery. I don't know if the rat ever came into the carpet and seats but we did find some rat droppings sometime ago. So, maybe it came inside first, then somehow jumped into t he airsystem and got trapped. Or maybe the car has many holes ( Toyota camry) and the rat was able to travel throughout the car

If your car has a cabin filter, try replacing it with one that's carbon-impregnated. You might also try Febreeze on the interior. Don't hose down the engine compartment, since you run the major risk of shorting out the ECM, alternator, and sensors. Try to locate where the rat has been and spot clean the area. Also, park the car facing into the sun and open the hood and windows. When you find one rat or mouse, there are more--get a cat.

A mouse is more likely than a rat. It can take 4-6 weeks for a mouse to stop smelling depending on temps and humidity. Merlin's muffler shop advertises they have a foam that they pump through your ducts and exchanger, may be an option along with that cabin filter.