2001 Nissan Almera surging idle

when engine cold idling good, but when get hot the idling goes up and down (surging) I replaced a used head and block and i start to get this problem, i exchange the head and block,install again and same problem..i bleed the air from the cooling system, replaced oxygen sensor, throttle body with tps and iac sensor.air flow sensor and the problem still there...please help thanks...to note a head and block comes with all sensors, i just have to add the external parts like alernator,ac compressor, throttle body,starter etc....qg18de engine