These cotton oiled performace filters have a habit of messing up Mass Airflow Sensors (MAF), they detect airflow by using a heated element (hot wire) and a resitive bridge to calculate air flow. The oil from the filter builds up on the heated element and changes the amount of current required to heat the element to its normal operating temperature.
What can fix these problems is spraying some carb cleaner down the inlet to clean up the hot wire element. Dont go in there with scrubbing brushes and clothes as its a sensitive bit of equipment, just a spay of cleaner over the element should do it.

If you can remove the MAF from the car to clean it then even better, maybe use some isoproply alcohol and give it a good rinse off.

This is of course if the S5 uses a MAF sensor?