TBH I think its a bit pathetic that people would jump to that conclusion but whatever. Don't worry those people are unhelpful in all threads.
From any research I have done it seems to be lack of compression in the engine. My e46 is a 330d and it runs sweet, drives nice and is pretty fast for a derv. Its economical too. So I dunno it may be that its down on compression but it drives fine. The piston would normally compress the air and thats whats holding the car but if its leaking or whatever its got no resistance. Or thats how I imagine it.