On 6/22/2012 4:11 AM, Scott Daniel - Turbovans wrote:
> I certainly think 'at rest position' is a lot more useful description
> than 'closed' for an AFM at idle or decel, or even engine shut off. It
> probably just drifts or flutters off rest position at idle.   Never
> closed fully so no air can flow at all.

The AFM moves significantly when idling vs. engine off.

The fuel pump depends on the AFM being open enough to close an internal
switch. With the engine off, the throttle plate is closed, the switch is
open, and the fuel pump is off. An idling engine keeps the AFM open
enough to close the switch, a significant difference in position.

The AFM opens even further during deceleration. On a manual trans, the
deceleration valve limits that by allowing unmetered air into the intake
manifold, which not only reduces the vacuum, but ensures a very lean
mixture, preventing backfires. (at least on an AC engine)