[Avatoy]

I've got this engine code of 0171, and I'm not sure exactly what it means. I've read other threads on O2 sensor or Air Flow/Fuel ratio sensors, and I thought it was my problem. My Avalon ran great for years on 87 octane, and then I got a check engine light. Several places couldn't pin it down to what exactly. One mechanic friend said it was my front air/fuel ratio sensor (bank 2, sensor 1), but he couldn't get it out. He said you would have to take the whole manifold out ($700), so I just switched to premium gas, and they seemed to do the job except some pinging in the summer while in the winter it ran perfectly. I let it go for 2 years, but now I worry that the pinging in the summer could damage the engine ( I was told this ) although the pinging only occurs when you really push it. In winter, it never pings. So I guess I need insight on what it could be, and what I should do. Thanks.