Spotted this and it sounds just like my problem! It took me 6 month to find the cause so I thought I would share the solution with you. The ECT sensor on the back of the inlet manifold

Mine would not start with the chip on, the fuel pump kept buzzing and the injectors clicked. No problem when it was hot, ran fine with the chip if only a little hesitant. The problem was that the ECU was not getting a signal from the ECT and the chip mapping was reliant on it, so it was trying to reset it constantly. The only affect it had without the chip was the ECU thought it was a cold engine and was always using extra petrol - hence the soot! My petrol bills halfed by replacing this £15 sensor