You are very lucky to have a KIA Carens, I have been using a Carens since 2003 and I purchased it Brand new from the agents in Sri lanka. and I am using it even today.
As I purchased First thing I did was to introduce the Soltron to the Petrol tank,It is an enciem which will get activated with petrol or Deisel and gives you more power and clean your engine nozells. It will give you more Milage and the engine will be very much smoother,and there wont be Black smoke.
The second thing I did was to change over to the K&N Air filter after the first 5000 km when I had to change the First Filter.It is a wonderful life time Air Filter, Once you fix it you can drive for 50,000 km without any cleaning and it gives more power and a better milage on fuel.
Try this two you will really enjoy the use of KIA Carence.