Regarding the stalling -
When you are n full lock, the effort required to get moving is significant;y greater than with the wheels in line, even more so due to the 4WD system trying to turn all 4 wheels at the same speed, which the wheels don't want to do.
Now, a van with no fault, you just have to push the throttle a bit harder.
You mentioned earlier that you have no throttle response,but free revving out of gear - this sounds like the van is extremely low on power, so this could account for the stalling - full lock is just too much for it in the current state.
To expand on my brief post last night (after a couple of pints!).
I looked at a van about a year ago for a friend which had a 0400 and 1228 faults. I don't recall it having a 1402 as well.
However, what I did diagnose was that the EGR is vacuum powered, and on the later (drive-by-wire) vans, the variable turbo is also vacuum powered. Although the fault code says wastegate, you actually have a variable vane turbo, which doesn't have a wastegate. The failed position on these turbos is minimal boost (hence the limp-mode effect).
Here's a wee ditty on how the variable vane turbo works. The earlier ones are more basic - once the manifold pressure gets to a certain level, that pressure is used to open the wastegate and dump the pressure. If these fail, then the wastegate stays shut, and you get mega performance (and something will go bang). The variable vane type rely on vacuum to drive the vanes to the position demanded by the ECU. Low boos position needs low vacuum, high boos needs high vacuum, so if you have a vac fault you get minimal boost.
The van I was looking at I could temporarily fix by disconnecting the vac pipe at the vac accumulator (plastic ball, towards teh rear of the passenger's side of the engine). Once the vacuum had been re-established, the van ran OK, until randomly the glowplug light stated flashing again.
In then end, the owner sold the van whilst I was away on a business trip, so I never discovered the eventual culprit.
By isolating various sections of the vacuum system, and seeing what (if any) faults clear you or your specialist should be able to narrow it down.
There's a steel pipe right in front of the engine, running vertically, which is part of the vac system. You can get to it from the driver's side (blind, but you can feel it). There's a 'T' point on this pipe which has a rubber cap n it. Commonly used to connect to cruise control kits (not really applicable to later drive-by-wire vans). It may be worth checking that this cap hasn't perished & fallen off..
It does sound like a nightmare, and as far as I could tell there's not much in the way of decent information about the vacuum system, so it will need a persistent and clever mechanic to get to the bottom of it (and quite probably a fair bit of luck!)
HTH
Dave
