it is in the plastic elbow in the intake hose just after the air filter (if its stock,) if not stock, it may be in the hose somewhere after the air filter.
Check to see if it is plugged in, and the plug is making a good contact.
The MAF (Mass Air Flow) is the big round thing in line with your intake air going to the turbo.
The MAT (Mass Air Temp) is a small sensor inserted in to the line. Stock was in the plastic elbow just befor the MAF sensor. The number was 16231141 but is now discontinued