Engine running lean, no vacuum leaks
 

Bought my 07 GTC a couple months ago. Overall the car has been great, but it has a couple issues that have been stumping both of my mechanics. I get occasional CELs which come and go seemingly at random. The codes are usually a combination of the following:

P0171 (sometimes) - System Too Lean Bank 1
P0174 - System Too Lean Bank 2
P2436 - Secondary Air Injection System Air Flow/Pressure Sensor Circuit Range/Performance Bank 2

The car has been smoke tested, and there are no vacuum leaks. I used my scan tool and noticed that at idle, the bank 1 STFT hovers around 0, and the bank 2 STFT is closer to 8%. Definitely seems there is something going on with bank 2. The o2 sensors seem to have readings in the normal range (~0.45v).

Today I had something very strange happen-- the idle got very lumpy for a brief moment, the car threw a bunch of pending misfire codes, and the traction control light came on. My mechanic told me that he saw something similar happen and that the codes were electrical in nature. Maybe I need a battery?

Anybody experience anything like this, or have any thoughts on what to look at next?

Could it be a failing vacuum pump?