Something I don't understand about tuning VE?
 

I've got EFILive, and have been logging and adjusting VE for several months now, and I am getting pretty close on the Ltft and STfts, but it keeps changing, and I can't seem to get quite as close as I want , <5% on the Ltrim's. Why is that? Ok, I know first thing everyone shouts is I need a WB02 to tune it right, and i understand that the narrowband o2 sensor are crap for WOT tuning, but shoudn't you be able to at least tune for part-throttle using your stock 02's and by going from the LTFT/STFT ?
And one thing I don't understand about tuning with a wideband. When you get done, your car is going to be running off your stock narrowband o2's anyway, because that's what the PCM uses, so what's the point in tuning with a wideband, except of course for PE during WOT ??
If someone could please enlighten my dumb ass, I sure would appreciate it!
thanks y'all

When tuning for 14.7:1, they're ok. The problem is, in closed loop the car cycles from rich to lean over and over. It never runs a steady 14.7:1 AFR. In open loop (with a WBO2), it runs a steady 14.7:1 (or whatever AFR you set it for). It learns by observing the variance in the closed loop AFR swings.

The other problem is, there's bound to be day to day variance in VE when dealing with weather changes and the heat soak issue the IAT is subject to in the stock location. It's never going to be perfect day after day. Just get it close and don't sweat the small stuff. ;)

Just as a side note, the 02's are really only binary sensors, their range is limited. How well they can actually read the further away from Stoich (14.7:1) that they get can cause problems. If the values sway too far, sometimes a lean condition can actually read rich and vice versa. Hence the purpose of the WB that allows you to read beyond the capabilities of the stock 02s.

SSpdDmon is right on about the environment. Just driving from one SMALL state to another on the same day can affect your IAT and MAP due to altitude or a drop in pressure. Even when you fill up your tank it can throw your trims off due to the cooler temp of the fuel.