you say you changed the turbo, but you have not said what you replaced it with,
ie, a recon, or a new turbo,.....But my guess is that you have replaced it with a used one....If so, that's your problem,
these renault turbo's are notorious for this kind of failure,
You sound as though you know what you are doing as you have gone for all the right things there,
A leak in the intercooler is known to very often preceed failure in turbo and EGR valve, Then the engine will start drawing oil from the crank case, thus making it impossible to stop the engine by any normal means,putting it in gear and stalling it is then the only way, when you cleaned the intercooler is it possible that you left some residue in there as they are very difficult to dry out,
Let me know how you get on, as These Renaults are one of my pet subjects,