Good work tjts1. I was not even aware of the pressure sensor for the EGR. So if I understand what is going on during the test sequence, the butterfly valve strangles the engine briefly and the pressure sensor measures the vacuum, then the EGR valve is opened and the pressure sensor measures the reduction in vacuum due to the exhaust inflow. That explains why the filtered air approach works, and why my suggestion would not work. Thanks, now figure out how to fool it, please. :-)

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'97 E 300 D