[tech]: idle specs on a 2.0L 16v cis-e?

[jason@scirocco.org (16V Jason)]

At 06:52 PM 1/24/2002, Michael Abatzis wrote:
>so, jason (since you seem to be the only one reading this thread), you 
>would agree that setting the duty cycle/bypass screw slightly lower than 
>normal would be the solution? or at least on the low end of normal?

Well, "slightly lower" than where it should have been for a 1.8, 
right.  But how can you be sure it was actually in the right place for a 
1.8 in the first place? ;)

The trick I would do is to let the car idle at normal operating 
temperature.  Then disconnect the electrical connection to the idle 
stabilizer valve.  Set the idle speed using the bypass screw so that the 
idle will be just slightly higher than where it should be -- say, 
1000rpm.  The reason I suggest doing it slightly higher rather than dead-on 
is for three reasons:

1.  Setting the mechanical idle higher allows more flexibility for the ISV 
to compensate for idle under cold conditions.

2.  Setting the mechanical idle higher helps the ISV to more quickly (and 
easily) stabilize idle when, for example, coming to a stop where the 
engine's speed is rapidly approaching idle.  Rather than having to quickly 
let a lot of air through the ISV to keep the engine from stalling (i.e. if 
the mechanical idle was set to 700rpm), the ISV would only have to pull 
down the idle 50rpm or so once the car stops.

3.  It lessens the chance for stalling under all conditions (including #1 
and #2) by giving the ISV more room to add air to the intake stream to 
compensate for your dumb-ass launch. :)


>as for the ignition...i don't have my bentley with me, but i guess it 
>doesn't really matter how it knows what the idle speed is... it has to do 
>it somehow. i can think of indirect ways, but seems it would be easiest to 
>measure it off the ignition somehow.

Agreed.


>btw, that wasn't what i meant about real knowledge-just a concrete answer 
>instead of hypothesizing (though that's half the fun with these cars, i guess)

That's all the fun.  You never quite know what the fuck is going on. :)

Jason





>-michael
>
>>>  that's how i understand it. the idle speed itself is not adjustable, per
>>>bentley. the computer has the correct speed hardwired, and it's your job
>>>to make everything right in order to get there. so it'll switch duty
>>>cycle to make the idle speed right
>>
>>Right.  It's always going to try to idle at the same speed.
>>
>>>. and yes, it should still idle at the right speed, but your tolerences
>>>would be less since the the computer is already working to correct for the
>>>maladjusted bypass screw.
>>
>>Bingo.  If the correct idle speed has to be reached by a duty cycle outside
>>the computer's ability; then idle gets messed up.  In this case, since the
>>engine would be pulling more air, the aux air bypass would be letting more
>>air in.  If the idle screw was closed too much for the aux idle valve to be
>>able to compensate for it, the engine will idle too low.
>>
>>
>>>  anyone with real knowledge want to weigh in on this one?
>>
>>Well, I do have "real" knowledge, technically, as I've read the Bosch fuel
>>injection book from cover to cover.  The problem is that every iteration
>>from different manufacturers have different sensors telling the computers
>>different things.  Some deduce idle from a crankshaft position sensor (the
>>CIS-E on my Mercedes, for example -- which also uses the sensor for a
>>separate ignition computer that has 100% control over timing).
>>
>>The problem I have with our logic is that I don't know how our KE-Jetronic
>>computer knows engine speed.  The hall sensor goes to the ignition
>>computer, so that can't be it....  (unless it goes to both?)
>>
>>Jason
>>
>>
>>
>>
>>>-michael
>>>btw, my idle miraculously cured itself with the apparent end of winter
>>>here in the ATL.
>>>
>>>>From: 16V Jason <jason@scirocco.org>
>>>>
>>>>Your thinking does make sense -- I think. :)
>>>>Unfortunately I don't have my Bosch manual in front of me -- but lemme ask
>>>>everyone:  Is the idle speed adjusted by the duty cycle?  Or (if my
>>>>understanding is correct), does the duty cycle just indicate whether the
>>>>idle air bypass screw is adjusted properly?
>>>>
>>>>If I'm right, and the computer knows idle speed, and changes duty cycle to
>>>>keep it where it's supposed to be (but can only do it within certain limits
>>>>and therefore you have to check the duty cycle to see if the screw is in
>>>>the right range), then Michael's right... the duty cycle would be higher
>>>>than it was in the 1.8... which would mean that the idle adjustment screw
>>>>should technically be adjusted to bring the duty cycle back down.
>>>>However,
>>>>if the car still idles perfectly, then the idle screw is set to a value
>>>>that is still within the aux air bypass's ability to stabilize it and
>>>>therefore it's not 100% necessary to adjust anything.
>>>>
>>>>...or am i just nuts? :)
>>>>
>>>>Jason
>>>
>>>
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