The leak-off and pressure tests can be inconclusive. Mine was 'fine' according to the simple tests but in reality the injectors were shot. The ONLY way we found out was by having them correctly bench tested by Delphi. Apparently they test something like 80 parameters!

A Delphi agent will also be able to test the IMV at the same time to see if that's at fault. (it is a likely candidate in my experience)

It does seem very expensive just to test the parts - but the alternative is to spend even more on swapping parts 'on a hunch'. With TDCIs it's always wise to get a proper diagnosis before buying random components - believe me, as I've been there, done that, and fitted several very expensive t-shirts!!!