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Old 11-11-2009, 12:12 AM   #1
LaphLaw
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Default High RPM at idle

Hi,

Lately, I've noticed that I'm idling, my RPM goes to about 2000 (normally it used to be around 1000). I haven't done any repairs or modifications lately that would have caused this. I don't have my AC going or anything like that, either. As soon as I engage the clutch and start moving, it drops back down to 1000.

Someone mentioned to me that it might be due to the cold weather, but even after driving around for 30+ minutes, it still does it.

One more thing that may or may not be related... just today, I was sitting in the drive thru ordering my food (Arbys), when it started idling at about 2000, so I had to shut the engine off so I could hear the guy. When I tried to start the engine again, my battery seemed to be dead (lights came on, and it attempted to start, but it my interior lights were dim as if a low battery). I had to push start the car. When i got home, I was able to start the engine no problem. Any correlation with my high RPM issue?

Any suggestions?

1999 SL1
Manual transmission

Last edited by LaphLaw; 11-11-2009 at 12:21 AM..

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Old 11-11-2009, 12:48 AM   #2
Ltech20
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Default Re: High RPM at idle

There are a few common things that cause high idle on the SL1 cars. Could be due to intake leak, Idle Air Control, or a few other less common issues. The battery going dead is most likely not related.

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Old 11-11-2009, 11:31 AM   #3
mattelderca
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1998 SC1
1996 SL
Default Re: High RPM at idle

My thought is classic loose or corroded battery conections or cables.
With the car running wiggle all the battery cables and harnesses under the hood and listen for the idle change. Sometimes when the battery is removed from the system, like with a loose terminal, the voltage drop causes the PCM to increase the idle speed slightly. YMMV

...
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1998 SC1 still running, FOR SALE cheap!
1996 SL, GONE but not forgotten
2005 Generic Silver Minivan (Kia Sedona)
2009 Nissan Sentra 2.0S

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Old 11-26-2009, 10:04 AM   #4
aa4lr
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1995 SC1
1999 SL2
Wrench Re: High RPM at idle

Quote:
Originally Posted by LaphLaw View Post
Hi,

Lately, I've noticed that I'm idling, my RPM goes to about 2000 (normally it used to be around 1000).
Have you replaced the ECTS with brass?

A failed ECTS, especially one that has leaked and corroded the ECTS connector wires will act this way. Also, gas mileage will be poor. That's where I'd start. Since this is an '99, what does the temperature gauge indicate? If it is stuck on cold or reading low, that's a dead giveaway of an ECTS and/or connector problem.

...
Bill Coleman
2001 Saturn SC2 Auto (3/13-...) "Yellow"
1999 Saturn SL2 Auto (11/09-...) "White"
1995 Saturn SC1 Manual (9/08-...) "Gold"
1994 Saturn SL1 Auto (7/94-1/04) 144,000 miles "Green"

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Old 11-26-2009, 11:47 AM   #5
Kirk
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Default Re: High RPM at idle

The previous reply from Bill was right on the money for my car. I had the same idle problem in my 1999 SW1. I removed and cleaned the EGR, throttle body and IAC. I verified the IAC was functioning when the key was cycled on and off. Made no difference. I replaced the IAC with known good one from another car. No difference. I removed the intake air temp sensor and tested the ohms, verified they dropped when heated with a hair dryer. It is the same part number as the engine coolant temp senor so I replaced the ECT with the good IAT sensor. My ECT was broken at the copper end, so I bought a new sensor and installed it in the IAT position. I disconnected the battery for 1/2 hour to clear ECU settings. When I started the car the RPM's were normal. After warm up it idles at 950 RPM. Before the repair my temp gauge never went to the 1/4 mark. Now it runs between the 1/4 and 1/2 marks.

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Old 11-26-2009, 01:16 PM   #6
SLCraig
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1996 SL2
2000 SW2
Default Re: High RPM at idle

Quote:
Originally Posted by aa4lr View Post
Have you replaced the ECTS with brass?

A failed ECTS, especially one that has leaked and corroded the ECTS connector wires will act this way. Also, gas mileage will be poor. That's where I'd start. Since this is an '99, what does the temperature gauge indicate? If it is stuck on cold or reading low, that's a dead giveaway of an ECTS and/or connector problem.
Just to add my 2 cents. If my temp gauge read weird at all, (high or low), I would immediately diagnose as a bad t-stat...

...
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2000 SW2 5MT. 133KMs. Gone, but not forgotten.

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Old 11-26-2009, 08:28 PM   #7
aa4lr
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1999 SL2
Wrench Re: High RPM at idle

Quote:
Originally Posted by SLCraig View Post
Just to add my 2 cents. If my temp gauge read weird at all, (high or low), I would immediately diagnose as a bad t-stat...
True enough. But the 96 and later S-series cars derive the gauge reading off the ECTS. If the ECTS is sending bad data, it will mislead the PCM into sending the engine the wrong mixture, which can cause the high idle. If the gauge reads low all the time, then replacing the ECTS is the first course of action.

If the ECTS and connector are ok, the next step is to look for an intake manifold leak as the source of high idle.

Once you know the ECTS is fine, then, yes, an odd gauge reading implicates the thermostat.

...
Bill Coleman
2001 Saturn SC2 Auto (3/13-...) "Yellow"
1999 Saturn SL2 Auto (11/09-...) "White"
1995 Saturn SC1 Manual (9/08-...) "Gold"
1994 Saturn SL1 Auto (7/94-1/04) 144,000 miles "Green"

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Old 11-27-2009, 09:28 AM   #8
signal7
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1998 SL
1999 SL
Default Re: High RPM at idle

Quote:
Originally Posted by mattelderca View Post
My thought is classic loose or corroded battery conections or cables.
With the car running wiggle all the battery cables and harnesses under the hood and listen for the idle change. Sometimes when the battery is removed from the system, like with a loose terminal, the voltage drop causes the PCM to increase the idle speed slightly. YMMV
I would second this suggestion as a possible cause. My 99 used to do the same thing intermittently until one day the positive battery terminal was so corroded it fell off the battery. Put in a new battery and it never did it again.

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