P4 ECM #1227748 questions

[Ludis Langens]

Nick McAlpin wrote:
> 
> I also figured that if I had a
> vacuum leak, it would idle much higher than expected (even with
> the IAC fully shut).

The V6's are prone to cracking the EGR tube.  (I think your L4 doesn't
have such a flex tube.)  Even with a large crack (1/16 x 1/2 ?), the ECM
is able to eventually bring the idle down to normal.

> So all that really happened is the 300rpm I added to the minimum
> idle speed, is now added to the high-rpm idle thing that the ECM
> seems to be doing.
> 
> Why is the ECM doing this to me??  for some reason, with no
> other change apparent to me, the ECM stepped the IAC all the way
> out to 2300rpm.

The ECMs of that generation don't command a specific fast idle speed.
Instead, they simply open the IAC x counts beyond the learned idle
position.  Not x% more air flow, not x% pintle movement, not x% more
steps, but simply x steps.  This means that the amount of additional air
depends on the normal idle IAC position.  Going from position 10 to 40
is probably a much bigger change than going from 110 to 140.

Try adjusting your minimum idle speed down.  This should force the ECM
to open the IAC more during normal idle.  Hopefully that'll result in a
lower fast idle.

BTW, the ECM will keep the idle slightly high while the VSS registers
movement.  Only when the car stops moving does the idle go down to the
target rpm.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/


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