Blame it on the bossa nova
The potentiometer senses change in airflow, and modifies the signal sent to the EHA during post start and warm up phases of the running engine. First thing to check on my list is the signal at the eha ( electro-hydraulic aAcurator) the controlled leak that modifies the control side of the fuel distributor, and thusly the amount of fuel available to the injectors. If it floats and varies according to the normal startup sequence, and brief throttle blipping causes an approx 10ma variation, the potentiometer is not the likely cause.
The idle speeds you spoke of are the inverse of normal, making at least two other items suspect: the thermal sensor and air leaks in the intake system or injector seals. Check those first.
This fuel system will not tolerate random checks and scattered approaches to diagnosis. You and your service technician must be willing to follow the proper sequence, from battery voltage available to the computer through every logic step necessary to the particular event you are pursuing. Only if those tests fail to bring a solution should other areas be examined. Of course, if there is an obvious problem, like a broken hose or wire, fix that first.
Otherwise, the bossa nova is just a dance.