See Figure 1
The auxiliary air regulator lets extra air into the intake manifold during engine warm-up which allows the engine to run smoothly while it is cold. As the engine warms up, a rotary valve inside the air regulator twists shut slowly, cutting off more and more air intake until almost none is passing through the unit.
To test the auxiliary air regulator, the engine must be cold. Unplug the fabric covered air intake hose (not the one that leads into the intake air distributor). There should be suction at the hose. Cover the hose: engine speed should drop. After a reasonable amount of time (time will be longer in cold weather), the suction should diminish until it is almost nonexsistant. If the regulator does not close at all, disconnect its electrical connector and connect a test light to the terminals of the connector (not the regulator). With the engine running the test light should light. If it does, the auxiliary air regulator is probably defective.