2000 Infiniti G20 IAC MOTOR

I was having the same problem w/ my 2000 G20t, plus my gas peddle was slightly sticking every now & then. I thought it was my alternator or battery at first because my check engine light had not came on, but after disconnecting the battery & the car was still running, we ruled that out. We tested the battery & it was still good. The check engine light came on after we reconnected the battery, so I got AutoZone to read the code and "Idle Air Control Valve/P0505" popped up. I replaced the iac valve and it runs fine. About a week after replaceing it, the Check Engine light came on again. I took it back to the same shop that installed the new valve & he cleaned the throttle body. The car still runs fine & the gas peddle has stopped sticking, and he turned off the light. A couple days later, my check engine light came on again. I got AutoZone to read the codes & I got 2 different codes, P505 (dealing w/ idle air control) again and P0171 (dealing w/ fuel injection system). The Autozone rep said it could be bad gas, so I bout some fuel system cleaner & added it to my gas tank. I will be going back to the shop hopefully today so see what they say about the other code. I was told it could be a falty connector w/ the iac valve. This is fustrating!!