Hmmm... Codes 1171, 0137, 0157 DO NOT indicate the air flow sensors. They are lean condition, low voltage O2 sensor bank1, and low voltage O2 sensor bank 2. Obviously, a malfuntioning or misfed MAP or MAF sensor could cause a problem, but these codes are specific to a lean condition explicitly. I think 0137 and 0157 are side affects and 1171 is your "real" code.

Okay, so it's lean. That's either not enough fuel or too much air. Can you tell if the condition occurs under boost or under vacuum? Maybe you want to buy a boost gauge for the A-pillar- it will look cool and could help diagnose this issue. This one should work well:

http://www.brandsport.com/trd-00602-83100-002.html

An intake leak could cause lean under vacuum, rich under boost. It is also possible that the gasket leaks under vacuum and seals under pressure, and could explain your lean condition.

However, I would look toward low fuel pressure at this point. Perhaps something went wrong during installation of the S/C kit. Check out the fuel pressure regulator to make sure everything is okay... you can also put a gauge on the fuel line to measure the pressure.

A scan tool that feeds live sensor data could tell you rich or lean in real time; combined with a boost gauge you could determine if the lean condition occurs under vacuum or boost. If it's under boost, it's likely a fuel delivery problem (like low fuel pressure).

One more thing makes me think it's fuel pressure: I'm pretty sure the VX has a MAP sensor in addition to the MAF sensor. If there was a discrepency between the readings, there would likely be a seperate, specific code. To find the MAP sensor, go to step 8 of Tone Monday's install instructions.

http://www.tonemonday.com/Storage/isuzu_sc_install.pdf

IT IS MISLABELED as the MAF sensor. That is the MAP sensor.
Incidentally, the other sensor is also mislabeled, it's the Ion Sensing module.

Anyway, I hope this helps.

Nate