I understand the test as you've outlined it, having been a VW CIS technician many years ago ( CIS was VW's version of this Bosch injection system) However; if replacing the EHA makes the symptoms go away ( which it has twice before ) my original question remains: what makes the EHA fail? I sectioned the first failure and discovered that the o-ring that seals the adjuster had disintegrated and clogged the reed valve inside the EHA, keeping it from floating under the direction of the field coil that responds to the input current from the control unit. The replacement unit lasted about 3 months, as has the second replacement. I speculate on possibilities such as contamination/corrosion failures in the fuel lines, voltage spikes/drop-offs, and bad luck. Any possibilities that I'm adjusting the mixture for a weak injector and overloading the EHA, causing it to fail prematurely?