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Old 08-24-2010, 11:20 AM   #1
ch3no2
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Default PCM? What else could it possibly be?

I have a '94 SL1 with a 5 speed manual trans that at first glance appears to have the classic Saturn high idle (1200 -1400 rpm) except that it refuses to be fixed. Instead of posting the entire horror story which would take more space then most would care to read I will skip the 6 months of code reading etc. and will list breifly what has been replaced or done. Hopefully someone will see something I have missed. Replaced....ECTS (twice), ECTS wiring, thermostat, TPS, IAC, EGR valve, EGR solenoid, Intake gasket, MAP sensor and most vacuum lines. Labor.....Proved there are no vacuum leaks by using a smoke machine, removed and cleaned throttle body, Cleaned or replaced every connection at sensors.
None of the sensors were replaced without having a code indicating it to be a problem at the time. I did find multiple vacuum leaks at first but to my suprise fixing them didn't help at all. The idle does sometimes go higher and stay there untill I come to a complete stop. IDoes anyone have any suggestions? Is there a way to test the PCM?

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Old 08-24-2010, 11:35 AM   #2
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Default Re: PCM? What else could it possibly be?

Find a cheap junkyard & pick up a compatible PCM & swap it to see what happens. Bad PCMs are rare, but possible.

*edit* another thought - the idle is controlled by the PCM through the idle air control valve. You could unplug the IAC in the fully closed position and see if it still idles high.

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Old 08-24-2010, 11:49 AM   #3
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Default Re: PCM? What else could it possibly be?

Wouldn't it be easier to block the little hole in front of the throttle plate? The one that provides supplemental air for the idle air control valve (IACV)?

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Old 08-24-2010, 12:25 PM   #4
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Default Re: PCM? What else could it possibly be?

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Originally Posted by fdryer View Post
Wouldn't it be easier to block the little hole in front of the throttle plate? The one that provides supplemental air for the idle air control valve (IACV)?
Why? If the OP's statement implies that the idle returns to normal when the car comes to a stop, it's running perfectly, and there's nothing to "test".

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Old 08-24-2010, 12:27 PM   #5
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Default Re: PCM? What else could it possibly be?

If it is not broke, don't fix it.

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Old 08-24-2010, 01:16 PM   #6
ch3no2
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Default Re: PCM? What else could it possibly be?

Perhaps I wasn't clear enough in my post. The idle is never normal. When stopped it is at 1200 - 1400 rpm. It is sometimes higher than that, up to 2200 rpm untill I come to a complete stop, then it will go back down to 1200 - 1400 rpm. I did block off the port for the IAC but the idle didn't change. This made me think there has to be air getting in somewhere, but I couldn't find a vacuum leak and the smoke machine couldn't either.

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Old 08-24-2010, 11:48 AM   #7
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Default Re: PCM? What else could it possibly be?

Quote:
Originally Posted by ch3no2 View Post
The idle does sometimes go higher and stay there untill I come to a complete stop.
This is normal. If the idle is 800-ish when the car is not moving, and 1200-1400 when the car is coasting, it's idling exactly as it was designed and built to do when it rolled out of the overhead door at Spring Hill.

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