I've had the same issue for the past 2 years, in my case it isn't the egr valve - although i have turned the valve round so that it is now inactive, this seems to give me better mpg and certainly improves acceleration.
As for the light, it comes on whenever you're going at high speed and under load (ie a hill or fast acceleration), when you put your foot on the clutch and drop the revs to zero it goes off? If so it's the same as me - i've put questions up on the forum and no-one seems to know the exact problem. I think there is too much pressure builds up in the engine under load and so it limits itself.
I've just managed to develop a slight fix. Below and behind the egr valve, at the top of the turbo you will see a long thin metal bar attached to the top of the turbo by two nuts. This is the actuator for the turbo wastegate. If you loosen the left nut a few turns and slide the waste gate attachment to the left, then tighten the right nut across again this opens the wastegate ever so slightly. So far this seems to let some of the pressure escape enough to prevent the light come on. I still need to test it on a long motorway journey, but i've managed short motorway journeys without the light coming on, when it normally would do. If you turn the nuts too far the wastegate will open too much - you'll know if this happens because you'll have no power in the car at all, struggle to accelerate.
You should be able to see the actuator bar in the pics below.
