535d: EGR valve causing engine stalls but ok when unplugged

Hi all... I just started having some trouble with the EGR valve on my '04 535d. When idling, the car will almost stall, then kick back into life, then stutter again, etc, until eventually it just dies. Every time it's doing this, I can watch the EGR valve opening and closing.

No fault codes are present via INPA.

Removing the EGR vacuum hose and blocking it off (with my thumb) has no effect. But if I unplug the EGR (by taking off the electrical connector plug) the engine runs fine. (shouldn't this give me a fault code?) It's like it's being sent a faulty signal from the ECU?

Does anybody have any ideas what might be causing this?

(I've previously already done an EGR-clean, MAF & MAP sensor clean, all filters etc)

Cheers
Chris.

Update: the throttle body (which sits in front of the EGR) was full of oil. Opened it up, cleaned it out with WD40 and contact cleaner, then put it back on the car. No luck, the problem still exists. Seems like it's a spurious signal being sent from the DDE?

I've left the throttle plug disconnected, but this is obviously only a very temporary fix... can anybody suggest where to next from here?...