who knows whats wrong with my saab?

[joseph455@btinternetecom]

its a saab 9-3 2.2 diesel at times it really losses all power the engine management light comes on and there is alot of smoke comes from the back it happens most if your going up a hill or doing a constant speed for a few miles any ideas i have changed the turbo and still has made no difference any help would be good thanks
have have taken it to 3 people to fix and none know the problem thats why i am on here and why so many parts have been put on.