another philosophy question

I knew there was one more question that I wanted to put down. Here it is:

Say you and a friend are hiking when suddenly your friend falls and breaks his leg. You don't have any cell phone reception and oyur friend can't move. You tell him that you will be right back and you run back to the car. When you get there you still don't have reception and the car won't start. You notice a car close to yours and happen to see that the keys are in the car also. Would you take the car? What if the owner of the car comes back before you can get the car back? Is it considered stealing?