The first one is to wonder if the fuel filter is uni directional and if so was it installed the right way round.
After watching your video I had different thought. The Duratec engine uses a bypass air valve for idle control and before I changed to throttle bodies I had a problem with this valve. The Zetec engine also uses a similar system. Basically the principle of the thing is that when the engine is cold, or the aircon (I know you don't have aircon) is turned on, etc, the valve opens to let more air into the system, a little like opening the throttle a tiny bit. When the engine is cold it is already getting more fuel so that all balances out and when the engine is hot the ECU, via the sonda lambda sensor, sees a weak mixture and adds more fuel to compensate. In addition to this the spark may be advanced and retarded to help adjust the idle speed.
To my mind you have all the symptoms of a sticking idle air control valve. I found this video in a Google search.