look for spilts in pipework to and from turbo and intercooler...check intercooler has not got a hole in it. I may be wrong but I think your turbo is not getting cooled air and is going into limp mode,the airflow meter is coincidence. BTW not all fault readers are the same...I had a similar prob and it was the 3rd garage with an up to date reader that pinpointed it.
d
February 2012