02 sensor cause for running lean?

[jakes97gs]

Hey i just got a 97 tsi with some mods and the a/f gauge (cheaper gauge probably not real accurate) is showing the car to run lean. the car has some error codes but i was told the rear 02 sensor was probably doing it as the cat has been deleted and the 02 sensor placed into the a welded bung on the pipe. is it possible for the o2 sensor to be sensing the dirty exhaust not being cleaned by the cat and leaning out the motor in an attempt to fix it? thanks guys

 

[92AWDHX40]

That narrow band will just blink replace the sensor leaning out, whats wrong with the car? If its fine i would never mind that gauge. No codes i would just drive the car.

 

[jakes97gs]

i have 5 codes: p0443 evap control system purge valve fault
p0125 closed loop fuel control insufficient coolant temp
p1105
p1104
p0403 egr flow ckt malfunction...
im not really sure what to think of these. ill check on the 1104 and 1105 but it seems like the other codes are from deleting egr or something like that.

does anyone know if these codes can cuase motor to run lean? any help would really be appreciated