The adjustment you are talking about would control the leakage rate of the EHA. The EHA is a controlled leak of lower chamber pressure.
The reduced pressure in the lower chamber is called differential pressure. This is what you would be screwing with. The dynamics of the pressure make it something I wouldn't want to screw with. If it is wrong the normal reason is either an internal fuel distributer restriction or one inside the EHA itself.
The differential pressure is so sensitive that it is what is used for electronic fuel control. The EHA dumps more or less fuel depending on the current passed through it. The differential pressure is .4bar with the EHA disconnected. The action of lambda from full rich to full lean gives about a .1bar correction to either side so the range should be .3bar (lean limit) to .5bar (rich limit).
I once had a car with corrosion in a large connector carrying the wire from the starter to KE controller. The car would start and idle great and all of a sudden the thing would go pig rich and die (if one didn't hold the rpms up with black smoke streaming). Watching the EHA current found that during the event the EHA current went to over 60ma. Knowing that the only normal condition to use such a current was starting enrichment, I found the problem while tracing that wire. A current that large changes the differential pressure to over 1bar. Quite a difference from the lambda ability to correct.
Bosch Master, ASE Master, L1
33 years MB technician