The first thing I would like to do is give you a brief explanation of the codes and the particular repairs from the past.
06 22 07 CODE P0171 - PERFORDMED CARBON BLAST & CLEANED THROTTLE BODY
This code number P0171 seems to be the common denominator in all of your on going issues with the exception of the air fuel ratio sensor failures. This code means that the air fuel ratio for engine is not getting enough fuel for the amount of air that is entering the engine combustion chambers. When you see this particular code by itself It usually indicates either an intake leak or restricted injectors. In some rare occasions when air fuel ratio sensors start to fail, it can set a false P0171 code. I'm actually surprised that the repair that they did with cleaning the throttle body and doing a carbon blast or cleaning resolved the issue. Based on the dates that you indicate.
08 11 10 NO CODE AVAIL - INSTALLED AIR FUEL SENSOR BANK 2 SENSOR 1
03 11 11 CODE P1130 P0125 P1135 REPLACED SENSOR ABOVE
03 16 11 CODE P1130 INSTALLED AIR FUEL SENSOR BANK 1 SENSOR 1
INSTALLED NEW THERMOSTAT
The bank 2 sensor 1 replacement was probably due to the engine codes P1150 or 1155 this is a fairly common repair. Air fuel ratio sensors are known to go bad on this engine. On March 11, 2011 the sensor that should have been replaced for these particular codes P0125 and P1130 and P1135 would have been bank one sensor one. This is either a typo or they replaced the wrong air fuel ratio sensor which surprisingly enough is fairly common. The P0125 code is not a thermostat problem that probably was replaced unnecessarily. That code P0125 comes on only as a confirmation that the air fuel ratio sensors are failing and are not recording proper data given the engine coolant temperature the computer is monitoring.
To recap the air fuel ratio sensor issues are as follows: you have 2 air fuel ratio sensors Bank 1 and bank 2 these are mounted directly in the exhaust manifolds just before the catalytic converters. Bank 1 when it fails, which is back by the firewall will set codes P1130 and P1135 and occasionally the P0125. Bank 2 which is up by the radiator and contains the bank 2 air fuel ratio sensor and sets the codes P1150 and P1155 when it fails and occasionally P0125 depending on the temperature of the engine. These air fuel ratio sensors are used to monitor just that the air fuel ratio of the burned exhaust mixture. If the engine starts to run lean or rich the sensors will detect it. Based on the content of the exhaust, and set the proper codes to indicate a rich or lean condition. There is a third oxygen sensor that is located after the catalytic converters and is used to monitor catalytic converter efficiency. This sensor should not be an issue and there are no codes indicating that the converters are inefficient. So you would not have any issues with that sensor at this point.
This brings us to the current problem dated April 10, 2011 and April 18, 2011. If the exhaust was replaced to correct the check engine light on and the code P0171 in my professional opinion this was an inaccurate diagnosis and repair. The reason for this is because even if the exhaust was leaking due to cracks in the exhaust the cracks would have to be upstream of these air fuel ratio sensors in the actual manifold itself in this is extremely unlikely and virtually impossible. Replacing or repairing anything in the exhaust downstream of the sensors to correct a P0171 code is just plain wrong. If the exhaust was being replaced or repaired due to leaks, this is a different matter.
I have seen some mass airflow sensors that get contaminated and will cause the lean condition code. In my opinion because this P0171 has been an ongoing problem There might be an intermittent issue or intake leak or possibly injectors that are slightly restricted or going bad. This engine does have injectors that get restricted and fail on occasion. Usually this will be accompanied by misfire code but not always.
If the exhaust was replaced to repair the P0171 code I think that you need to politely request your money back or your original exhaust system Reinstalled back on your car. Based on the same code setting on April 18, 2011 It's obvious that was not the fix and was an inaccurate diagnosis. This mass airflow sensor can be cleaned with relatively good success as a temporary fix to see if that resolves the lean condition code. Let me know if this clears things up for you. Hopefully I did not bore you with too much detail but an educated consumer is something to be feared. Educate yourself as much as possible. If you need any other input or advice on this issue Feel free to reply and I will get back to you.