Corsa cdti white smoke

Hello all
I'm not a mechanic I'm just trying to find out a few things regarding a problem with my Corsa 1.3 CDTI

As it feels like the garages that ive been to so far have just changed parts and not really investigated the problem yet I've still been charged for it


I have a colleague who is a mechanic by trade he's now had a thorough look at some things and has found an issue which I'll get to later

Anyway on cold start irrespective of ambient temperature it was previously firing irratically and clouds of whitish smoke (he says it's unburnt diesel) pours out,
This goes after the engine gets hotter

Also sometimes after a short run on motorway 20 mins I've been in stop start traffic and the engine has struggled at low revs and can sometimes become irrattic

So first the glow plugs were changed then one fuel injector was deemed to be faulty and new fuel filter fitted after they ran injector cleaner through the old one

Now my mate has had a look yesterday and found that the egr valve was staying open at low revs, checked it and found that it was permanently on and when engine was revved it opens more but sticks as the spindle returns

So at the moment this has been taken off until I have a new one for him to fit

He's being thorough and checking everything step by step
( pressure tested the cylinders, tested glow plugs and injectors although this problem has been there in cold and hot weather , also checked and cleaned all electrical connections)

This has improved the idling and has more power although the smoke still occurs

When he checked the injectors the new one is feeding a lot more diesel than the others almost double he said he wasn't at all happy with this ,
Is it something he can sort or will it need to go to a commercial garage or main dealer?

So I'm guessing this could be the cause of the smoke that's still being emitted
I'll get the egr replaced this week.

So if anyone can give me any pointers for what to look at next
I'd be very grateful