So the car just started doing this recently... I keep getting DTC code P0174 (system too lean) and the car idles a little rough every so often... But it only happens when the car is at an idle and never seems to happen on a cold start, only on a start after the car has been driven for a bit... Dosent happen while the car is being driven...

So im wondering what could be causing this? Could it be in the tune?

 

P0174 is the bank 2 equivalent of P0171, click here to see the possible causes.

Since it is only apparently affecting one bank I would first check for exhaust leaks in the manifold, or near the O2 front sensor on bank 2.