Default [Q] Charging on AC but shows USB

Initially my phone started to charge slow since a week with the original charger and cable came with N4 in the box. I googled and got to check in the battery settings as if it shows AC or USB. Its showing USB and charging quite slow. I flashed yesterday factory image after deleting everything but still it shows as USB.
One more thing, when i connect the charger it shows AC and after a few seconds it says USB and sticks to it.
After connecting the charger it acts as the charger is powered on and off 3-4 times whereas i dont turn the power off/on.

Any help.
Nexus 4 MAKO