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Old 07-24-2009, 12:34 PM   #1
rsg3
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Default Engine Revving Randomly / High Idle?

Yesterday, while sitting at a light, my RPMs went up from the typical (750rpm) to about 1500rpm without me touching the gas. After checking to make sure the gas pedal wasn't stuck on the carpet, I gently touched the gas to see if that would 'un-stick' it. It revved normally, but went right back to 1500rpm, eventually climibing to 2000rpm or so. When the light changed, I started driving, and everything was fine (normal idle) the rest of the way home, so I thought little of it.

But this morning on the way to work, it did the same thing, except it revved to about 3000rpm. The next time it idled (after about 10 minutes of highway driving), it was normal.

My initial thought was a sticking throttle body plate, but it seems like tapping the gas pedal would 'free' it, at least temporarily, and that doesn't explain why the idle would've gone up yesterday. I cleaned the TB about a year ago and it wasn't very dirty to start with.

It's a '99 SOHC 5speed with 71k miles. I have a ScanGauge and the TPS data look normal and there are no lights or codes. Car runs great otherwise, idle was never high before this. Haven't changed anything lately except thermostat (Stant 195) and coolant. ECTS is brass.

Could it be the IAC valve? A mechanical issue with the throttle cable / body? Something else entirely? Thanks for any suggestions.

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Old 07-24-2009, 12:38 PM   #2
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Default Re: Engine Revving Randomly / High Idle?

I had the same problem. I hooked up my Scanner it read throttle plate was open at like 2.5% when closed so I replaced it, still had the problem then replaced the ECTS with a brass dealership one. No problem at all now. Also I disassembled and cleaned the TB.

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By the end of the night."

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Old 07-24-2009, 12:51 PM   #3
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Default Re: Engine Revving Randomly / High Idle?

There's also another trick to isolating the problem to a possible throttle position sensor (TPS); the next time the idle runs away, shut off the engine and restart it without touching the gas pedal - if the idle returns back to normal its a worn out tps.

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Old 07-24-2009, 12:57 PM   #4
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Default Re: Engine Revving Randomly / High Idle?

Well on mine I could physically lift up on the TPS and it would go away or shut the car off restart it, it would go away. But it didn't solve the problem replacing it and the ECTS did it.

...
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By the end of the night."

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Old 07-24-2009, 01:02 PM   #5
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Default Re: Engine Revving Randomly / High Idle?

I understand your situation but did you read the second to last line of the OP's first post where he replaced his ects?

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Old 07-24-2009, 02:29 PM   #6
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Default Re: Engine Revving Randomly / High Idle?

Watch your temp gauge when it does this. Even though you have changed your ects. My ects plug went bad and started causing this.

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Old 07-24-2009, 02:36 PM   #7
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Default Re: Engine Revving Randomly / High Idle?

No FD I didn't feel like reading. My eyes are broken and I can not read.

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Old 07-24-2009, 02:55 PM   #8
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Default Re: Engine Revving Randomly / High Idle?

ECTS. I'd take it out and take a look at it, it can still corrode or go bad even if it's brass, so yeah.

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Old 07-24-2009, 03:21 PM   #9
rsg3
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Default Re: Engine Revving Randomly / High Idle?

Thanks for all the replies! I just drove the car again and it didn't do it, so I'll have to wait and see. Next time it happens I'll turn the car off and back on and see what it does.

I'm thinking it's probably not the ECTS because I did look at the water temp on the ScanGauge when this happened initially, and it was normal. But who knows, maybe the ECTS output just goes out of range for a fraction of a second. If the on/off thing doesn't isolate it, I'll definitely have a look at the ECTS.

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Old 07-24-2009, 06:15 PM   #10
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Default Re: Engine Revving Randomly / High Idle?

I would spray some electrical contact cleaner on the ECTS plug and see what that does before removing the sensor

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Old 08-02-2009, 10:44 PM   #11
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Default Re: Engine Revving Randomly / High Idle?

I have the same issue with a 2000 SL. I have replace the TPS, ECTS...at start up it revs up to about 3K and then drops to 2K..and just maintains at that RPM. I have read else where that it could be air leaking into the fuel injector ports? I haven't done any trouble shooting just read it...oh this isn't my car a lady friend's car.

Zach

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Old 08-02-2009, 10:45 PM   #12
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Default Re: Engine Revving Randomly / High Idle?

I hope I didn't try to take over the thread, just same problems.

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Old 08-03-2009, 04:28 AM   #13
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Default Re: Engine Revving Randomly / High Idle?

http://www.saturnfans.com/forums/sho...lve%2Fdiagnose

This covers the debug steps quite well. My 3rd gen single cam had all of these things happen.... one at a time.

Good luck.

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