I've not done it on a Z.. The ECU will be in Closed Loop during Idle, ( after the Engine is Warm ) so the O2 Sensor Feedback for each bank, will be correcting the Fuel Mixtures... They will be 'Dithering' above and below the Magic 14.7 Fuel Mixture. This Cycling above Stoch and Below Stoch Feeds Fuel and Air to the Cat's during the Cycling..