[Shotimes] RPMs gone crazy.......????

[Marlene Doyle]

Maybe the author of this subject line  will step forward and restate the importance of the Malfunctioning Idle Speed Controller::
 
Subject: Re: [Shotimes] DAGNABIT....This High IDLE is killing 
  me....Anyone please....some input
Date: Thu, 13 May 2004 09:51:51 -0500

This is NOT correct. Don't confuse throttle opening with idle speed.
Different throttle openings are required depending on engine load to
maintain constant RPM's. This was the reason for the IAB in the first 
place.
The PCM does not know or care what the drag is. What it wants is the 
engine
to idle at the programmed RPM in the look up table. Remember too, this 
is
adjustable with a LPM chip. The PCM will always attempt to hold the 
idle
speed steady. If the TPS voltage indicates the throttle is closed then 
the
PCM adjusts the IAB to maintain the programmed idle speed. Once the TPS
voltage goes over 1 VDC the PCM shuts the IAB completely. The wide idle
speed variation is from the changing load on the engine and the 
inability of
the IAB to compensate fast enough or at all to the new conditions. Or 
that
the voltage returning from the TPS is over 1 VDC and the PCM does not
realize that you are still in a idle situation. When the "load" is 
removed
the idle will readjust. You can verify this yourself. Let the car idle 
with
the A/C in the off position. Then turn it on without touching the gas 
pedal.
Turn the steering wheel too. It is an additional load. Watch your tach 
to
see what the RPM's do. After the initial fluctuation of the RPM it will
settle down to the exact same speed.
Our problems with the SHO's idle ( I think?) are caused by multiple 
small
problems and is MUCH harder to trouble shoot. A small bit of resistance 
in
the voltage loop to any of the engine sensors can cause a .25 or .5 VDC
offset to the signal and then the PCM programmed logic is ALL 
confused!!!
Somebody found a .5 VDC offset in the TPS and after fixing that, the 
idle
returned to normal.

Maybe time to get a break out box and start checking things!
.
.

> The engine PCM was trying to compensate for the extra drag.
> The PCM resets the idle parameters every time you shut the car off.
> If you start it with the A/C on and the compressor has extra "drag", 
it
sets
> the idle higher.
> A few minutes later when the compressor heats up and returns to 
normal,
the
> idle goes up.
> The PCM never resets or lowers the idle back down, it was never
progrsammed
> to deal with that condition.
> Result too high idle.






http://www.cardomain.com/id/snowwind
1990 White S H O:    Snowwind:  @319K..very stock, very OEM 
1991 Black S H O:    Bart:  @217K ..not stock, not very OEM.. tokicos/eibachs/SHOSHOP CAI/2nd fuel pump replaced 5/04





		
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