A small discrepancy in MAF isn't bad and you say that at 3000 rpm it provides about 850. This means it's working normally.
The most likely reason for the slow response on the MAF is because something is causing airflow to lag. The most likely reasons include sticking turbo vanes, bad vacuum lines/N75 boost solenoid, or bad actuator.
Check the article on checking VNT actuator function. If it's sticking or slow due to the aforementioned reasons, it will cause the airflow to be slow and cause the MAF reading to be slow.
Also possible are fueling problems. Check the fuel injection quantity IQ. There's a FAQ article showing how to do this.
The most likely reason for the slow response on the MAF is because something is causing airflow to lag. The most likely reasons include sticking turbo vanes, bad vacuum lines/N75 boost solenoid, or bad actuator.
Check the article on checking VNT actuator function. If it's sticking or slow due to the aforementioned reasons, it will cause the airflow to be slow and cause the MAF reading to be slow.
Also possible are fueling problems. Check the fuel injection quantity IQ. There's a FAQ article showing how to do this.