VE (SD) Tuning
Why is the VE table so important? At WOT the computer references the MAF, so who cares about VE?
Well, the VE table is referenced during ALL operations except for WOT over 4000rpm's. And I don't know about you, but I spend most of my time OUT of WOT.
Just as a reference, this is how the computer works:
You roll into the throttle and the MAP will sense a change in manifold pressure. This will cause the computer to check the VE table and provide an initial fueling correction with adjustments from the IAT. Then the computer checks air mass readings from the MAF and correlates this info with the VE calculation. Final fueling is then determined by an interpolation of the two.
So, when the VE is much closer to the required airflow that will be calculated by the MAF, then fueling is smoother, faster, and by nature more accurate.

This is why the VE table needs to be fully tuned.

Plus if the MAF fails, the VE table is soley used. Obviously...