Rechecked MAF readings when cold. Should have been around 17 - 18 kg/hr but our readings were 9 - 10 kg/hr. We had already discounted valve timing, air leaks, and egr. Fitted a MAF sensor and lo and behold the vehicle runs ok all the way through the rev range and temperature range. Extended road test proved ok. Rechecked live data and still only getting around 11kg/hr which is still lower than anticipated. Customer is going to run car to try it but I am not certain that we have fixed the fault or just masked it by slightly improving MAF efficiency. Time will tell