did you check if the oxy sensors are mixed up (wrong connections under the car), oxy sensor plugs cylinder row 1 connected to 2 and vice versa?
I once mixed that up when I changed the oxy sensors, so I connected the oxy sensor of right bank to the plug for the left bank exhaust and vice versa on my M70 V12 engine. Idle was terrible.
Both wirings and plugs coming from the engine are almost side by side under the car and mixing them up is possible.