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2001 eldorado,2008 DTS,2005 XLR, '96 eldo,'95 eldo,' 89 eldo,'78 eldo,'11CTS-V
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1,718 Posts
Discussion Starter #1
I
I'm working on a fast idle issue on my '89 eldo, and find the plunger on the ISC extended and not retracting.
Removing the ISC, I can get the stepper to retract (and extend) by applying 12 volts to the stepper motor.
But there's an internal switch that opens when the throttle is depressed (not touching the pindle).
What does this switch do? Mine is open in any actuation.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,275 Posts
I
I'm working on a fast idle issue on my '89 eldo, and find the plunger on the ISC extended and not retracting.
Removing the ISC, I can get the stepper to retract (and extend) by applying 12 volts to the stepper motor.
But there's an internal switch that opens when the throttle is depressed (not touching the pindle).
What does this switch do? Mine is open in any actuation.
=======================
there are two parts that must work properly -
and be set-up properly to control the idle speed -
ISC - Idle Speed Control motor -
and TPS - Throttle Position Sensor -

there is a special procedure for setting up each component that MUST be followed -
 

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Registered
2001 eldorado,2008 DTS,2005 XLR, '96 eldo,'95 eldo,' 89 eldo,'78 eldo,'11CTS-V
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1,718 Posts
Discussion Starter #3
Y
Yes, I'm aware of the TPS specs, but the question is, what's the job of the switch on/in the ISC?
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,785 Posts
It's called the open throttle switch. It tells the PCM when the throttle is open (as the name implies) and deactivates the ISC motor because it is not needed.

Do you have any DTC's?
 

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2001 eldorado,2008 DTS,2005 XLR, '96 eldo,'95 eldo,' 89 eldo,'78 eldo,'11CTS-V
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1,718 Posts
Discussion Starter #5
No, DTC's. Idle WAY high (1600). Will check TPS settings next.
 

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2001 eldorado,2008 DTS,2005 XLR, '96 eldo,'95 eldo,' 89 eldo,'78 eldo,'11CTS-V
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1,718 Posts
Discussion Starter #6
Let me see If I've got this right.
I've steppered the ISC pindle down (all the way in) via ECM OVERIDE. Engine stalls.
Throttle bellcrank not touching the pindle.
Go to ECM DATA and spec for TPS is +.6; just at the spec. limit (+.5).
Prior to this last test, I've replaced the ISC because the original ISC internal switch wouldn't close; the pindle would cycle in and out (on the bench).
Have not driven the car. News at 11.
 

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Registered
2001 eldorado,2008 DTS,2005 XLR, '96 eldo,'95 eldo,' 89 eldo,'78 eldo,'11CTS-V
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1,718 Posts
Discussion Starter #7
I
It now idles at 650 (in gear) and 800 (in neutral).
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,737 Posts
If not mistaken, the ISC uses 5 volts as a reference voltage not 12. If that's correct, you shorted out the old ISC. The idle speed should be virtually the same in or out of gear. With the ISC fully retracted the car should idle, not stall. Usually around 400 to 450 RPM. Either the throttle body is gummed up with carbon or the minimum idle screw on the throttle body is set too low.
 
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