Hello VF members! I'm new to the forum, but have found it pretty useful in the past, so i thought i'd put this question out there.

I just replaced the Mass Airflow Sensor on my '98 T5 (as per the check engine code i got from the shop) and now whenever the car has been sitting for a while (1+ hour) and is rev'ed up to about 4000 RPM, the engine surges and lurches, much like as if it were on the verge of stalling.

The car runs perfect at lower RPM, so i'm wondering if its something weird about the MAS that i installed, or maybe dirty injectors/bad fuel pump? Any thoughts on the problem are greatly appreciated!

Thanks everyone!