The blinking low fuel light is telling you that the car has just failed the EVAP test for a large leak. The fault code is P0455. The gas cap could be loose, or the purge valve may have failed. There are a number of possible problems. The reason the light blinks only when the car is idling is simple. The self-test for a large leak is performed only when the car is idling at a stand-still. Also, the test only occurs if the fuel tank is between 1/4 and 3/4 full.