Hello Ron! I use my powerwasher to clean the mats--laying them on the concrete--then draping them over the deck railing to dry or I take them to the car wash, hang them--the car wash has spring clamps to hang them--and wash them with the power car sprayer.
Ron, if you have rubber floor mats in the car you can brush or power wash them off and use a mild detergent like you would your car. If they are cloth, you can do the same. We use a scrub brush too on our car mats. Hope this helps.
We don't have a power washer so when I do mine, I take them out and put them on our driveway then pour a mix of Dawn and water on them and scrub them with a brush. Then just rinse them with a hose and hang them to dry. If you don't have something to use to hang them, you can try what I do. I put then over the back of a plastic outdoor chair, then clean the chair when I'm done with basically the same method. Wishing you the best.
Our car wash has clips on the wall so you can hang them up and clean them with the high pressure washer. You can also use dish soap and a hard scrubbing brush.
Scrub brush and dish soap in soapy water then hose off
I have the weather tech rubber floor mats. I use dish soap and water to clean them but when I am all done I rub baby oil on them to get that new look shine again. Helps with spills also.