Error Code P1174
A friend of mine bought a 2006 Chevy Cobalt SS (n/a) a couple of days ago. She took it for a test drive, at which point the check engine light went on. Dealership tells her not to worry, they will have it fixed and ready for her to pickup the next day. When she got home from the used car dealership, a check engine light came on again. Used my scanner and found out its a p1174, fuel trim cylinder balance malfunction. We took it back to the used dealership, and talking to the mechanic we determined it was likely a vacuum leak or faulty O2 sensor.
They claim to fix it, fast forward a few days, and the light comes back on. Understandably, we are getting quite frustrated with having to go back and forth to get this issue sorted out, so here is my question:
What would be the best way to go about fixing this? I'm pretty good with fixing cars but she lives an hour away and obviously I dont want to fix the dealership's screw ups, so I would like to know the best way to explain to their mechanic that resetting the system or erasing the code clearly is not the way to fix it (as this is our third time having them "fix" it).