I was driving on the interstate at about 60 mph when my escape began idling by itself. Then suddenly my speed dropped to 40 and then minutes later to 20 mph. Then it wouldn't move. I pulled over, let the car sit for a minute and then started it again. The problem persisted. I kept having to stop and turn the car off. I couldn't even make it home as the car would no longer accelerate over 20mph. What could this be?