The CD lists a 10% fixed duty cycle as indicative of a faulty airflow meter position sensor (the diagram points to the potentiometer), and the part was worn thru in the area of resting position (idle zone), just as stevebfl expected.
The 10% duty cycle is what first led me to this part.
A possible explanation is that the function(s) of this part evolved in the ensuing 4 years. (84-88)
Hopefully Steve will elaborate on the role of this housing when he has the opportunity to check out this part.
Personally, when I check and adjust the system this weekend, if the idle problem is gone, I am willing to ascribe success to replacement of this part. Just the 15 minutes of uneventful idle with no hunts to 1500 or 2000 RPM Sunday night has caused high expectations.
Even if this subassembly only contributes during warmup, it transmits a voltage to the ECU, and you would be amazed at the unintended consequences a stray/screwball voltage (or grounding of an intended voltage) can cause on an entire system.