Can a car air filter be washed? Well, washing it with water is not recommended, but you can clean it. As long as it is not too dirty, or too worn out. If it is, you should replace it with a new one.
To clean an air filter you will need is a shop vacuum, and a air compressor. First use the vacuum to clean out any bugs, leaves or anything else caught in your air filter. Take the time to clean out each of the accordion-like folds. Next you should probably go outside or at least somewhere you don't mind blowing dust over everything to finish cleaning your air filter.
Take the air compressor, make sure it has a compression head on it to add more power, and begin blowing the dust out of the air filter. Carefully blow out each fold before turning it over and blowing out the flat side as well. After you have finished blowing out as much dust as you can, you may want to go over it with the vacuum one more time.
Before you finish, take the vacuum and clean out where your air filter clips into your car's engine. Or if it is too hard to get the vacuum hose in there, you can use the compressor to blow out any debris and dust instead.
Washing the air filter is not recommended, simply because once it gets the filter wet, making it hard to dry it out properly. But in a pinch, it may help extend the life of your air filter.
Remember, washing it with water will not get all the dust and debris out of it as effectively. Vacuuming and blowing it out is the most efficient way to clean your car air filter, and not ruin it's performance.