Ah.... Maybe you now have the 'engineer fix' like we used to have on the VCR in the early '80s (yes... I am old enough to remember them.. Just!).. They'd play up for ages.. You'd get the engineer out to look at it, and it would behave like a new unit, then as soon as he went away.. bang.. faulty again.
Maybe just some crap in the fuel that was blocking the injector for a bit and has cleared? I would go with the 'heavy right foot' clearance method.. Just boot the bugger for a bit and hope it still works
