VALVE ASSY, VACUUM SWITCHING, what's this for ?

[jondee86]

The small VSV pictured above is installed at the factory with one tube
connected to the throttle body and the other tube connected to a source
of filtered air. It will normally raise the idle speed about 100 rpm when
it is active. That is not enough air to cause rough or loping idle.

According to the actual model of your car, the idle-up VSV can be active
when one or more of the following occur...
- at engine start up
- when head lights are ON
- when brake lights are ON
- when rear screen heater is ON
- when heater fan is ON
- when A/C is ON (some cars have a separate VSV for A/C).

There is no fault code for the VSV so it is most unlikely that it can cause
the check engine light to come on. Loping idle is almost always caused
by a blocked thermostatic idle-up valve, or a vacuum leak that raises
the idle speed high enough to initiate fuel cut (>1700 rpm).

Cheers... jondee86