P219A - Bank 1 Air/Fuel Ratio Imbalance

[96Firebird]

2013 Equinox, 2.0L 4cyl, 114k miles. Bought it off my sister, drove it for a month and this light came on. Needed NYS inspection done, so I changed the air filter (thing was nasty), cleaned PCV valve, cleaned MAF sensor, reset fuel trim, and had the timing chain replaced (notorious on this motor). Code went away long enough to pass inspection, but has come on again recently. I clear it, it comes back on a few drives later.

Can't really get much info from the internet on this one, I'm not exactly sure what to check as far as how to diagnose. I have a Bluetooth OBD2 reader with the Torque app, so I can read sensors real-time. The pre-cat O2 sensor looks fine, reading looks like a sine wave bouncing from high to low to high to keep the A/F ratio where it needs to be. Post-cat O2 sensor seems good too, usually stays constant around .6V-.8V.

What else can I check, or what else should I be looking for? My inspection is good for a year, but I want to get the annoying service engine light off.

 

[repoman0]

Check out short and long term fuel trims -- long term should be near 0, it's okay if short term bounces around. The code could be tripped by long term trims going over/under a threshold, which would indicate that the AFR isn't anywhere near where open loop mode expects it to be for one reason or another.

114k miles is near O2 sensor lifetime. If that's not it then it's probably fuel related -- if swapping injectors is easy on that engine, switch bank 1 and 2 and see if the code follows. Could be plugs or coils too, might as well swap them all.

 

[96Firebird]

There's only 1 bank, being an inline 4. I checked the fuel trims, short term is bouncing around, long term is pretty steady around 0. I wish I could tell which cylinder the imbalance was on, would be easier to diagnose... I'm going to try some fuel system cleaner, long shot but I read it worked on another forum for a completely different vehicle. Part of the issue might be that it was sitting for a while when my sister was trying to sell it, so the fuel might have gotten old/stale and maybe clogged an injector? It would even help if I had a misfire but I don't.

I might as well get the O2 sensors too, while I'm at it.