This is probally the best info I hav read

If the TPS is set negative (below 0.45V at idle) when you open the throttle slightly the ECU will think the throttle is not open, apply the fuel over-run routines and cut fuel at 1400 or 1800 rpm. This will often cause the revs to cycle between about 800 and 1800 rpm. Also the car will be jerky when driving around at low speed.

If the TPS is set positive (over 0.45V) then the fuel over-run routines won't work, and also the ECU will not run the correct idle routines to keep the idle steady. It's better to have the TPS adjusted slightly negative, but setting it to 0% if fairly easy with datalogging. Otherwise aim for 0.45V.