Via some google searaching I understand it better now. There are two systems:
-Swirl valves
-Intake manifold switchover system

I can't post a link so here's a cut and paste.

Swirl valves

Ford workshop manuals Workshop Manuals Haynes auto repair manuals Free car repair manuals Engine Car repair manual



Ancillary Auto Mechanic Description Emmy Ford workshop manuals Workshop Manuals


Item
Part Number
Description
1
-
Swirl valves

The swirl valve system from the Mondeo remains unchanged.

The swirl valves reduce the cross section of the intake ports in the lower engine speed range, thereby swirling the intake air.

The improved swirl of the fuel/air mixture makes the fuel/air mixture easier to ignite. Fuel consumption and exhaust emissions are reduced as a result.

The plates are adjusted by means of a vacuum motor on the intake manifold.

The swirl valves are closed when the engine is not running.

Intake manifold switchover system


Item
Part Number
Description
1
-
Flaps - intake manifold switchover system
2
-
Intake manifold switchover vacuum motor
3
-
Swirl valve vacuum motor

The flaps of the intake manifold switchover system allow the length of the inlet tract to be varied in order to allow engine speed dependent resonance charging of the cylinder.

The flaps of the intake manifold switchover system are open when the engine is not running.

When the engine is started the vacuum generated is applied via the solenoid to the vacuum motor of the intake manifold switchover flaps.

The flaps of the intake manifold switchover system are closed.

Now the inlet air is exclusively obtained through the cylinder specific inlet port from the intake manifold.

When engine speed is increased to around 4500 rev/min, the flaps of the intake manifold switchover system are opened.

When engine speed is reduced to around 4300 rpm, the flaps of the intake manifold switchover system are closed.

This allows the inlet air to flow out of the other intake pipes, via the cylinder specific intake pipe and the cylinder specific flap of the intake manifold switchover system.

 

Interesting that your 2006 2.0 engine is equipped with both systems (IMRC & IMTV). Here in the USA (North American models) our 2005+ 2.0 Duratec engine is only equipped with IMRC. The USA 2.3 Duratec engine is equipped with both, IMRC and IMTV.


IMRC - aka swirl valves:
The IMRC actuator is monitored by the PCM via a positional feedback circuit to/from the actuator. If the IMRC actuator fails to operate, a DTC will be set. Most typical is P2004. Faulty components are usually the (1) solenoid (2) vac hose cracked/disconnected (3) wiring (4) actuator.

IMTV - aka intake manifold switchover system:
The IMTV actuator is NOT monitored by the PCM via a positional feedback circuit to/from the actuator. If the IMTV actuator fails to operate, no DTC is set. It is possible that the IMTV solenoid wiring is monitored by the PCM, and if wiring is defective, a IMTV code could be set. I have never seen anybody report any IMTV code.

 

Even more interesting, and something to investigate, that info. claims that your version CLOSES the 'swirl plates' (tumble flaps) when the engine is off.

That is opposite the normal operation of my 2.3 with the dual controls, which defaults to the OPEN position for the swirl plates so a failure doesn't affect operation to a large degree.

Operating lever for those plates near the head is normally UP on our version for open, pulled DOWN to close for low RPM use when the engine is started.

 

Update: I bought the relay off Ebay and it fixed the problem and my mpg came up from 39 to around 43 under similar driving conditions.
Then a few months later the mpg dropped back to 39mpg and I eventually worked out that the thermostat was not operating correctly so I fitted a new one. An "interesting" job in terms of access. That brought the mpg back up to 42mpg but then it started dropping again.
Then I found that the engine was going from the max oil mark to the min mark in about 8 days of use. Engine had done 245,000 miles so decided the game was over.