Hi all. I’m posting here because I’ve run out of options. My 2005 T30 2.5petrol idles at around 1800rpm and surges up and down esp when cold. Have changed ETB, maf sensor, crank and camshaft sensors. Even changed ecu with used on from EBay. No change. No fault codes either. Relearn idle also no change. Local Nissan dealer also unable to solve issue. 
Any new inspiration greatly appreciated or it’s change vehicle time. 

I have had issues with the throttle pedal potentiometer before and gave symptoms similar to this
You have to 'dial in' the switch which rotates to a given setting when you measure the volts between a certain range....problem solved at little if no cost

Also, check your earth straps from the battery to chassis, chassis to engine and also gearbox as these break and can cause strange faults

Finally look for vacuum leaks which can also cause the engine idle to hunt

Thanks Trevor for your reply. I have replaced the Earth connections and looked for leaks, but will double check any way. The idle issue is the same even with the pedal position pot disconnected, so I concluded that was not the issue, but will measure the voltage as you suggest.