Then it's dieseling (self fuelling)
Check all your oil levels, seals on turbos and compression on cylinders. Try not to drive it anywhere as it runs a chance of running off and the only way to stop it will be to dump the clutch in 5th when the car is standing still and hope the gearbox can take it. Needless to say doing all of this whilst it's ragging it's head off is quite stressful.
compressions on cylinders? whys that as when i bump started it (roll down 2nd gear release the clutch, bang car started) the car started up straight away and we left it running for over half hour and then turn it off then waited a few seconds and started it, it did struggle but it started.
oil level is fine, seals on turbs, we cant check that as i cant.
one thing that did come up when the it wouldnt start was "economy mode active" but then after a half hour of having it srated that message went away.