Crikey, how long has this topic been going .
I joined in a while back as I had the same symptoms as the original post.
So far I have fixed a fuel leak, replaced both lambda sensors among several other fixes and none have really changed anything. ( I thought I had fixed the fault but must of imagined or wished it)
Anyway after changing the lambda sensors, due to out of range readings, and not making a difference I thought to look at what would make the lambda go out of range. First thing that spring to mind was the egr valve being irratic sending irratic gulps of exhaust gas through, so I simply blocked off the valve and hey presto it runs lovely now.
Don't know if this helps anyone but I had to tell someone......