2001 ford focus (y reg) 1.4 16v.

car starts no problems, when warm and idling the engine seems to struggle and surge. have change idle control valve, map sensor, TPS, head temp sensor, oil temp sensor, inlet manifold gaskets, throttle housing gasket, idle control gasket, crank and cam sensor, ht leads, plugs, coil pack, did have air leak in oil breather hoses under injection manifold but have sorted, no eng managment light on.

depress the brake pedal and the revs lower on idle, according to scan everything is fine and operating, fuel consuption is high and oil consuption.

at a complete loss of cause, head gasket is fine no oil leaking externally, or in water, or on plugs compression is fine.

only other explanation i can think of is injectors, throttle itself,or valves are burnt out. what do you guys think?