What up turbo group. I been having a problem with my engine bucking/surging during driving at most time between 2700-3200 RPM and speed of 55-63 mph on 4th and 5th gear. My AFR gauge will go back and forth to 12.2 -15.7. If I just tap the gas pedal a little more it will stop. Other wise car runs great. I've checked all vacuum lines and replaced VAM. Timing is stock.I don't know were else to check? TPS, control module or internal waste gate maybe? If any body has any suggestion please help.