There are a few threads on this. I believe the problem seems to be getting the air flow meter to work with it. I'm having a custom one fitted next week, my Afla guy explained why they have these MAF problems but sadly I had no clue what he was talking about.
Ah right cheers Morte,im a bit unsure bout getting one if its going to nacker my maf up! only spent 170quid on one bout 6 months ago,if you could let me know the reasons your guy was talking about when you find out that would be great!cheers.