Thanks for the kick in the pants to monitor the EHA current. I made a harness to sit in between the car's harness and the EHA valve that I could plug my digital multimeter into. And I hooked up my fuel pressure gauges. I also recorded some numbers before and after. Mostly I was concerned with the before numbers with the EHA current, lambda duty cycle, and upper and lower chamber pressures in the fuel distributor so I could put everything back after I botched it up. All numbers are after the lambda values adapted and began fluctuating.

Before:

Idle
EHA current: -0.3 mA to +0.5 mA
Lambda duty cycle: 66% to 71%
Upper chamber: 80 psi
Lower chamber: 76 psi

2,500 rpm no load
EHA current: -4.5 mA to -5.8 mA
Lambda duty cycle: 46% to 53%
Upper chamber: 80 psi
Lower chamber: 75 psi

At this point, I pulled the EHA valve off, removed the plug, and adjusted the 2mm allen screw. Then I reassembled everything, adjusted the allen screw on the airflow meter to get zero current at the EHA valve at idle, and tested again. I did this four times, turning the EHA screw clockwise 1/6 turn, 1/4 turn, 1/2 turn, then back counterclockwise a bit, so that with the EHA current at idle set to jump back and forth across zero, the EHA current values at 2,500 rpm no load were closer to zero, and the lambda duty cycle numbers at idle and 2,500 rpm were closer to each other.

With the EHA allen screw turned clockwise about 150 degrees from stock and the airflow meter adjusted accordingly to compensate:

Idle
EHA current: -0.4 mA to +0.2 mA
Lambda duty cycle: 62% to 68%
Upper chamber: 80 psi
Lower chamber: 74 psi

2,500 rpm no load
EHA current: 1.3 mA to 2.5 mA
Lambda duty cycle: 66% to 72%
Upper chamber: 80 psi
Lower chamber 74.5 psi

Then I put everything back together, pulled up the carpet on the passenger side floor, hooked up my meter to read closed loop voltage from the lambda sensor, and took the car for a spin. Even without looking at a meter, I could feel right away the car was much more responsive on part throttle accleration. And the lambda voltage was almost always jumping around between about 0.3 volt and 0.7 volt, even during moderate acceleration. The only time it went lean was when I lifted off the throttle to decelerate, engaging the fuel cutoff. This is exactly what I was hoping for.

Thanks for all the help. This site is a great resource.

Patrick