Since you are getting a varying Duty Cycle, we may assume, for the moment, that the ECU and the EHA are operational. The throttle response symptoms suggest that the mixture is on the lean side. A spark plug check should confirm this; dry, clean plug: lean or OK; wet, sooty plug: rich.

Two things could contribute to lean response; the mechanical mixture adjustment (as mentioned above), and the lack of a motion signal from the air flow sensor potentiometer.

The mechanical mixture adjustment is located in a tower just in front of the FD. If there is still a plug in the top of the tower it will have to be removed to gain access to the adjustment. If no plug, a 3mm hex key is inserted and pressed down gently while turning slightly until the adjuster engages a screw underneath. Clockwise is richer; 1/8 turn increments, no more than 1/2 turn total. Keep a note of the number and direction of the turns.

The potentiometer is mounted on the side of the mixture control assembly next to the FD, and has a three wire plug. Pull the plug and check that the resistance between pins 1 and 3 of the sensor varies when the air sensor plate is pressed down through its range. If there is no change or if there is no continuity at all, there will be no enrichment signal to the ECU.