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Old 03-18-2018, 08:09 PM   #1
aygc271
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Default 2000 Saturn SL2, Self Revving Engine, Coolant Sensor or Throttle Position Sensor?

I'll try to keep this brief. The car has 144,000 miles, clutch is on its way out but still works decent, significant SES light exhaust issues but I don't think it'd be causing these problems. No check engine light is on. Essentially at stop lights when I neutral drop, the car periodically revs itself up to 4000 RPM and hangs there for awhile until I put it into gear and start driving. It doesn't happen all the time but pretty frequently. Often times if I don't keep the revs up while stopped, it'll crash all the way down to zero and stall out the car. While I'm driving, sometimes it'll start accelerating or hold speed like cruise control even with my foot off the gas. While stopped and while I'm driving, the temperature gauge is either a quarter way up like it's supposed to be, or it'll go to and stay on zero for awhile. The revving seems to be mostly happening when the temp gauge is at zero. When it stalls out, the car won't re-start until the temp gauge comes alive again.

I already cleaned the heck out of the throttle body and replaced the IAC . I feel pretty confident that I've narrowed it down to the coolant sensor or the throttle position sensor, but I don't know what way to go. I'm hoping with the wealth of knowledge on here you guys might have a suggestion. Do you think it'd be worth it to try and go to the junk yard and grab another of each? Or should I just buy new parts? I've never had a shred of trouble with it otherwise besides basic maintenance, and even though the car looks like hell, the engine is too low mileage to bail on this sweet ride. Thanks for listening.

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Old 03-18-2018, 08:23 PM   #2
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Default Re: 2000 Saturn SL2, Self Revving Engine, Coolant Sensor or Throttle Position Sensor?

I'll say it here, too... use live-data to avoid a lot of guessing. Look at TP, IAC steps, and MAP for clues. The engine can't rev up without excess air getting in there. This isn't an ECT issue, but you can quickly check the ECT sensor, too, with live-data.

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Old 03-18-2018, 09:32 PM   #3
Rez
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1996 SW2
Default Re: 2000 Saturn SL2, Self Revving Engine, Coolant Sensor or Throttle Position Sensor?

Checking to see if you have a brass or ceramic sensor would be an easy check. My sw2 temp gauge always read screwy until I replaced mine. Also my TPS needed replacing as well, but I was experiencing revs at idle and had a bad dead zone when I accelerated to 2000-2500 RPM.

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Old 03-19-2018, 11:06 AM   #4
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Default Re: 2000 Saturn SL2, Self Revving Engine, Coolant Sensor or Throttle Position Sensor?

aygc271, if you never replaced the coolant sensor, it's likely the original bullet nosed plastic one that fails on every S-series engine. When it fails, it cracks and leaks coolant out onto the connectors and fouls them. A green corrosion forms and prevents good electrical connections resulting in erratic signals. If you don't have a reader and aware of what to look for, you're not ikely to see anything unusual. It's just easier to remove it on a cold engine and examine it. The flat nosed brass replacement cures this problem while a fouled connector needs replacement.

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Old 03-19-2018, 07:58 PM   #5
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Default Re: 2000 Saturn SL2, Self Revving Engine, Coolant Sensor or Throttle Position Sensor?

As Billr stated, you have to have a LOT of air in the manifold for the engine to rev up to 4,000rpm in neutral or when the clutch is depressed.

When the TPS fails, the TYPICAL symptom is the rev hanging at about 2,000rpms. If the TPS is going out, there will be other symptoms as well. Misfires or poor acceleration. There should be a "Service Engine Soon" DTC that codes the PCM, poor fuel economy, and when you shut the car down it will immediately restart and resume a normal idle of about 750-850rpm.

Stalling is usually a symptom of a vacuum leak.

The coolant gauge going bonkers COULD be the failed ECTS OR a failing BCM. The BCM controls the gauge cluster on 2000-2002 Saturn S-Series. Usually, the car will not start and the "Security" light will flash or stay on, but this could be an anomaly that we haven't seen much of.

And on the off-chance: have you tried pulling the fuse to the Cruise Control module?(If you have Cruise Control)

While this may sound screwy, and probably not even close to the actual problem, the cruise is digital on these cars. Mine just stopped working, the other day, for no apparent reason. I was on flat ground. I had to turn the switch off and back on, to get the cruise to work again.

It floors the gas, when it is engaged, but there is a separate cable or pulley for the throttle body in that control module under the steering column. If that module has gone bad, it is possible the opposite could be happening, and the cruise would be opening the throttle. This should cause the gas pedal to depress on its own, which would explain the jump in revs without any other issues or a "Service Engine Soon" light.

...
"What does a Saturn owner do, at the gas station?"

"He checks the gas, and fills the oil....."

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