Sean writes:
>
> > Paul writes:
> > The cold idle circuit of most Bosch fuel injection systems incorporate
> > an "auxillary air regulator". When you start the engine, this valve is
> > open, allowing additional air (and hence gas) to be consumed by the
> > engine.
> >
> This is incorrect.  The auxiliary air regulator does NOT allow any more
> gas into the engine.  It also does NOT change the air/fuel mixture being
> burned by the engine.

I didn't say it did. I "allow(s) additional air (and hence gas) to be
consumed". At the higher idle, additional air and gas are consumed.

>
> All the air that flows through the air regulator has already been
> measured by the air flow meter, and so does not change the air/fuel
> mixture.

I didn't say it did.

>
> The only thing that the aux. air regulator does is provide a bypass to
> the closed throttle plate when the engine is cold to help overcome th
> e mechanical drag of a cold engine.  It is basically a fast idle device,
> very similar to an automatic choke, except that it does not change the
> air/fuel mixture.

I didn't say it did.

>
> The air/fuel mixture is determined by the computer, which notes how much
> air, how cold/warm it is, how cold/warm the engine is -- then the
> computer decides how much fuel to inject by varying the time the
> injectors are open.  Note that the state of the aux. air regulator has
> no bearing on how much fuel the computer injects.

I didn't say it had a bearing.

>
> You would be right to say that more gas is being burned when the aux.
> air regulator is open but that's only because the engine is cold and the
> computer notices that and sets a rich mixture.  It is not dependent on
> the auxiliary air regulator itself, though.

The aux. air regulator is simply faking that there is more air
entering the system than would be based on the throttle setting, and
thus the idle increases. More air and gas is being consumed at the higher
idle speed. The engine runs faster, and thus doesn't stall when cold.

The bottom line is that a bad aux. air regulator is often the
problem when a cold, Bosch FI engine stalls repeatedly.