In reply to a message from CJ95 sent Tue 17 Sep 2013:
John:
Thanks for the feedback. I’ve driven carburetored cars, but
was in my late teens/early 20s and do not remember any of
the carb-tuning basics.
What you are saying makes sense, but I wonder about the
effect of the EVAP system. IIRC, you capped off yours, am I
right?
If this is the case, your idle is never affected by the
carbon-canister, while my engine can breath through it.
I re-read the JDHT last night (again) and I noticed the
section on ‘Adaptive idle fueling trim’. See my other post
above.
Anyhow, there it says that if are no DTCs present the ECU
cancels purge flow and adapts the idle fueling. OK, now, if
I disconnect the O2 sensors, DTC FF44 comes, the ECU does
NOT close purge flow and does NOT trim fueling, will this
make the idle speed higher or lower?
Best regards,
Steve–
The original message included these comments:
The lower idle seemed to make sense to me. I know in the ancient
days of carbruetors, the speed of the engine grew faster as you
leaned the idle mixture…up to the point where the car would get a
lean roll to it, and finally die if you went leaner. I figured
defaulting the map to the richer setting would naturally make a
slightly lower, but stronger idle, like I experienced.
Now if moving your car to the richer map sped up your idle, you may
be on the rich side with the sensors hooked up? I’m not sure if
that would be possible, though. Just thinking out loud. Maybe
back to your temp sensor reading too cold? Or, your car could be
way on the lean side with the sensors connected, so the rich map
–
'95 XJS V12 6.0L, saphire/tan
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