Idle fuel mixture setting

[Walter Meares]

> Bohdan.L.Bodnar at att.com writes:
> > Idle actually runs richer than 14.7:1.  There are several reasons for
> > this (such as longer exhaust scavanging time at idle than off idle).  I
> > also know that some engines which do not use heated oxygen sensors run
> > open loop at idle;  this is because the O2 sensor will cool off and present
> > incorrect readings to the computer which will then cause the engine to
> > "hunt" as the air/fuel mixture varies wildly.
>  
> Whoa, be careful with the blanket statements.  I don't know about Fords, but
> GM stuff DEFINATELY tries to run closed loop at 14.7:1 at idle.  I think
> your statment applies more to earlier attempts at closed loop fuel
> control than it does to modern systems.  From an emissions standpoint,
> you'd want to be lean if anything at idle.
> 

I think the CIS-E on my Audi is closed loop at idle as well (85 4000S quattro).
Can't remember offhand what A/F ratio it tries to hold there, but stoich would
make the most sense.  

> -- 
> Jonathan R. Lusky  --  lusky at knuth.mtsu.edu

Walter

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