Thanks again GVK. What a level of service! Very impressive and sounds like good news. I assume that the three wires are, respectively, power feed & return/earth and valve-position? (will these be 5v or 12v?). So as long as the valve moves from time to time (which it will presumably,even though the blank is in there) the ECU should not detect any apparent problems. Does this sound correct?

Now I realise what is going on here I really really dislike the idea of pushing hot, dirty exhaust gas back into the intake so think I will fit the blank on my 2 litre TDi Mondeo anyway (even though everything seems ok at present). Its actually a friend's car which put up a fault light so I need to check his EGR type as its a 2.2TDi (also a 2007 mk3) but hopefully it too is vac operated.

Thanks again for the advice. Much appreciated.

Just out of interest, do you know which of the 3 wires is which? Also, under what conditions does the valve open on a TDi? i.e which sensors are involved in compiling the info that tells the ECU when to open the solenoid controlling the vacuum actuator; and what engine conditions trigger them?