kia sportage 2007 diesel suv

hi I have a kia sportage 2007 turbo diesel just had the gearbox rebuilt also put in a new mass airflow sensor as the car was running a bit rough. After the gearbox was rebuilt it was fine for a week but now I cant pull out of a junction and will not rev under load if you can get it up to 3000 rpm then the car will pull away like a rocket.Its as if there is a flatspot.Injectors have checked there is turbo boost. car idles lovely but its the low rpm that's the problem about 15 seconds before the car comes to life the only code I have now is C0700. I hope someone can help as im getting up 2 the 2000 mark and im not a rich man. Thanks