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Unlike a newer injection systems throttle switch, the D-jet's switch doesn't report throttle position to the computer. It just has two fairly simple functions.
1) Signals when the throttle is fully closed. This put the computer into the specially tuned idle mode. The emissions tests of the day were all performed at idle. The computer has a special adjuster on it that only affects the mixture at idle - each and every car was hand tuned at the factory with an exhaust gas sniffer and this knob. This allowed them to pass emissions without all the air pumps and other junk foisted on other cars, and of course made no difference on how the car ran off idle.
2) A low-tech electrical accelerator pump. Just like a carb car an injected car needs a brief fuel enrichment when the throttle is opened further. The simple way D-jet does this is to slide contacts over a sort of saw-tooth patterned set of contacts. Each time it makes contact it triggers an extra injector pair firing cycle (normally triggered by those switches in the base of the distributor). You only want that to happen when the throttle is opening, not closing, so those contacts are on a sort of friction mounting that pushes switches shut when opening and pulls them open when closing. However, this is a pretty subtle driveability enhancement. You can generally totally unplug that throttle switch and not notice much of a difference.
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