Hi

Always start with a few basic checks
Even so called profestionals some times slip up here.

Do a conpression test to make sure your engine is good mechanicaly before you get too technicial

If thats all good a fuel pressure test would be good---ok

Check all your multiplug conections

Make sure there are no air leaks and all the pipes are on the plenim

Check the Map sensor pipe and that there is no petrol contamination

Cheers Tim