hi, need advice please regarding my 52 plate Discovery 2 TD5

Although once going it drives well i have trouble starting it unless my accelerator pedal is to the floor and the engine cranked over by the key. It starts after about 5 secs and kind of builds up as if it is flooding.
It does feel flat when first accelerating too.

My garages 3 diagnostic computers could not hook up to the car computer to diagnose any problems which is weird also.

My thoughts are .. is it injector problem? Fuel pump? Or maybe even the engine management system needs program updating?

Has anyone else had this problem.

I want it re-mapped but cannot do this until it runs as it should.

Thoughts and advice greatly appreciated. Karl