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Old 04-25-2012, 08:15 AM   #1
raffy
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Default Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

I couldn't find any info specifically on this when doing a search. Once in a while, the idle on my 2000 Saturn SL will go up to 2000 rpm or so instead of dropping down to about 900-1000 rpm or so when crawling or 750 rpm when at a dead stop. This only happens occasionally; the vast majority of the time the idle will drop to 750 when coming to a stop like it is supposed to. I put in a new ECTS sensor a little over a year ago and the car has had its intake manifold gasket replaced due to the "drunken robot" that crimped it during manufacture. The car also has new spark plugs although it probably is time to replace the wires. There's no Service Engine Soon light on (at least so far), so no DTC codes. If I turn the engine off and then restart it, the problem always goes away (so far) and the engine idles normally at 750 rpm. A rather weird intermittent problem that's been happening once in a while for the last couple of weeks or so.

Otherwise, car runs fine, has plenty of power (for a Saturn S-series) and I'm getting 36 to 40 mpg driving to and from work and a little around town. There's 88,xxx miles on the clock so it's fairly low mileage. It's an SL so it has the SOHC engine.

So what do you think might be causing this intermittent problem? IAC valve? EGR valve? Or something else?

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Old 04-25-2012, 08:34 AM   #2
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Default Re: Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

TPS make sure that new part number matches old.

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Old 04-25-2012, 08:56 AM   #3
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Default Re: Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

Thanks, td! Is the throttle position sensor pretty much the only thing that does this or should I also look at the IAC and/or EGR?

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Old 04-25-2012, 08:58 AM   #4
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Default Re: Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

The self-correcting on shut off and restart almost always points to the TPS.

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Old 04-25-2012, 11:32 AM   #5
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Default Re: Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

You can test the TPS with a volt or ohmmeter. Richpin has a youtube video for the voltage method. For resistance, unplug sensor and probe between the center terminal and each of the end terminals. Move control through its range. If resistance or voltage change isn't smooth, replace sensor. Jumping around or moving forward, backward, and forward again, or dead spots indicate wear.

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Old 04-25-2012, 11:56 AM   #6
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Default Re: Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

Definitely sounds like the TPS to me. I would suggest cleaning the throttle body/IAC valve (probably overdue anyway) and testing the TPS. If the TPS tests bad, replace it.

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Old 04-25-2012, 02:22 PM   #7
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Happy Re: Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

I had a 1991 Olds Cutlass Supreme 3.1 that did the same thing and it was the TPS, fast forward 7-8 years later the TPS had to be replaced again.

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Old 04-26-2012, 07:57 AM   #8
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Default Re: Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

Thanks, guys! I think I'll go ahead and change the TPS since it's only about $30 or so. I did clean the throttle body a little while back using Amsoil Powerfoam while the engine was running. Might also need to look at the IAC valve and clean it as well. Like I said, so far it's a rare intermittent problem so it may take a while to figure out if it's really been solved by changing the TPS.

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Old 04-26-2012, 09:37 AM   #9
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Default Re: Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

While I'd bet money on the TPS, you should still test it, and get into the practice of testing parts before you replace them. This prevents unnecessary replacement and gives you a better understanding of things.

Not all tests are definitive, but the TPS test is.

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Old 04-26-2012, 10:06 PM   #10
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Default Re: Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

TPS more likely.

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Old 12-01-2014, 12:41 PM   #11
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Default Re: Occasional Intermittent High Idle When Slowing Down or Coming to a Stop

Quote:
Originally Posted by td1238 View Post
You can test the TPS with a volt or ohmmeter. Richpin has a youtube video for the voltage method. For resistance, unplug sensor and probe between the center terminal and each of the end terminals. Move control through its range. If resistance or voltage change isn't smooth, replace sensor. Jumping around or moving forward, backward, and forward again, or dead spots indicate wear.
guys - i have the same problem. lets say when i am driving at normal speeds around 40 miles and about to come to a red light or a stop sign, when i apply the brakes the RPM jumps up and then comes down.

i changed the TPS "ACDelco 21024706 GM Original Equipment Throttle Position Sensor" but that did not help. any suggestions?

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