Engine weird a/f ratio, need help.

RadioFlyer

Great input, and important information to know. Just think out loud here... It's happening in your closed loop operation. Closed loop targets AFR off your front O2 sensors and MAF sensors. Have you cleaned your MAF sensors recently? Have you done all the resets (idle speed reset, throttle body reset, etc)? I agree with you that it's not a tune issue if it's doing this with all stock parts/stock tune. A vac leak wouldn't be my first thought if it starts fine, and slowly drifts off. So I'd look at sensors, and start with what's cheapest to change - cleaning the MAFs, running a bottle of injector cleaner, clean your PCVs, doing all the ECU resets... Last thing I would want to try would be the O2 sensors, they're pricey. But how many miles are on your O2 sensors?