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1993 DeVille Sedan
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5 Posts
Discussion Starter #1 (Edited)
I week or so back I had some trouble with my 93 Deville not wanting to start, which I tracked down to the ISC motor not engaging the throttle enough on cold starts.

Well now it starts but the majority of the time the ISC is out of control and I am seeing very high RPM while at idle. I pulled the following codes:

E30: ISC RPM out of range
E31: Shorted MAP Sensor
E98: High RPM P/N to D/R Shift Under ISC

I can see the two ISC codes being thrown but what is the MAP sensor code all about? And is my only solution to this problem in replacing the ISC motor? I should also add that I've had issues with it ratcheting when I turn the car off.

Thanks in advance for the help.

-Justin
 

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Super Moderator
2010 DTS
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87,413 Posts
The MAP (Manifold Absolute Pressure) sensor is bad and may be causing the high idle. I'd replace the MAP sensor first since it is known to be bad (shorted).
 

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1991 Cadillac Brougham D'Elegance 5.7 Litre, 1994 DeVille
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6,796 Posts
What the ISC does is based off of other sensors so just because it's part of a code doesn't mean it's the problem. It could be acting strange because something else is telling it to, or yeah there could be something wrong with it. The service manual says how to test it.
Even when there is nothing wrong with the ISC you can still hear it move right after you shut off the car.
 

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1993 DeVille Sedan
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5 Posts
Discussion Starter #4
Thanks, I'll check out the MAP sensor and the Helms manual to see how to test the ISC motor. Would rather replace the MAP sensor since it's not quite as expensive as the ISC motor.
 

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1993 DeVille Sedan
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5 Posts
Discussion Starter #5
I found a MAP sensor on Rockauto for fairly cheap that I'm going to pick up. Do you guys think this will cure the high idle issue since it is throwing a code (shorted MAP sensor)? I wasn't going to buy a new ISC unless I find that the new MAP sensor doesn't solve the problem.
 
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