Any knowledge on 4M40 EGR valve function?

[quick6]

I have a '95 Delica and have had an issue with a constant haze of smoke at light to medium throttle opening the whole time I have had it. It is not thick but clearly visible, the motor uses no oil or water. A quick search led me to checking the function of the EGR valve which I found to be in good shape, moves smoothly and closes fully. I started it and observed the valve while the engine was running and what do you know the valve opens at light to medium throttle. So I disconnected and blocked the vacuum pipe (disabled the valve) and the smoke is either gone or reduced to the point I can't dee it, problem solved......
My question is, how is the valve supposed to work? What could cause it to open at the wrong time and is this what is happening? Should I just consider it fixed and move on, surely it's there for a reason?