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Old 07-09-2008, 01:21 PM   #1
jfr1111
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Default SL1 revving way too high at idle and while driving

The car's alternator had to be changed at 100k km and now, a few weeks later (car now has 102k on it) the car wants to idle very fast: the battery is still in good condition and is giving full charge.

To give you an idea of how fast it idles, if I'm driving around 50 mph and let go of the gas, the car hardly slows down and will settle around 40 mph. Stopping at red lights/stops has become problematic because of the force I have to exert on the brakes to keep it from going forward and the very choppy downshifting. While engaged on D it will idle at around 1.2k (while it would idle at 500-600 before the alternator died). It is a steady, but too fast idle. Engaging park will have the car's idle surge up to 2.2k and then come down to 1.2k.

The car has been to the mechanic and had its ECTS changed last February. It would idle very roughly (up and down) but now it behaves as if the car is always very cold (and thus producing a way too rich mixture) or the alternator is strugglign to keep the battery charging (but it is charged). The engine coolant gauge hardly registered anything on my 80 miles drive home today (pretty much all hills without any stopping in 76F weather) while it usually settles below the mid point. The coolant level is stable just below the Full Cold line when engine is cold but I had to top it off a bit a month ago. All signs thus point to the ECTS crapping on me again, but I had it changed for a new Saturn unit last February ! This cannot be ?
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Old 07-09-2008, 07:31 PM   #2
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Default Re: SL1 revving way too high at idle and while driving

Would help to know what year the car is. If it's the third generation (years '98-'02), it could be an intake manifold gasket leak. It's fairly common, though the symptom is usually a rough idle. You can find it by spraying some carb cleaner around the intake manifold near cylinder #1. If the idle changes, that's your best bet. IMG failure should also set the Service Engine Soon light. Get the codes read at Advance or Autozone for free, then post the codes here. If it is the IMG, it'll be a P0301 - cylinder 1 misfire detected.

High idle can also be caused by a failing TPS - Throttle Position Sensor, located on the throttle body. Next time the idle is high, try rapping the TPS with a screwdriver handle. If it straightens out, you probably need a new TPS.

You can also try turning the car off and then back on to see if the high idle stays or goes away. Let us know.

Although I've never heard of it happening, the IAC (Idle Air Control) valve could be bad, letting too much air past the throttle at idle.

Only other possibility I can think of is a dirty throttle body. They're super easy to take off and clean.
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Old 07-09-2008, 07:57 PM   #3
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Default Re: SL1 revving way too high at idle and while driving

With "only" 100K km, it almost certainly has to be an '01 or later. It's quite possible that in the process of R&R the alternator, the intake manifold was "nudged" giving rise to a vacuum leak at the gasket.

Regarding the "always cold" gauge, it's possible the thermostat has gotten stuck open. Otherwise, it's possible the new ECTS is a victim of infant mortality, rare but it happens. Your mechanic should be able to compare the reading from the ECTS to a probe in the coolant expansion tank to determine if it is misbehaving.
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Old 07-10-2008, 05:09 PM   #4
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Default Re: SL1 revving way too high at idle and while driving

The car is a '97 SL1, so it cannot really be the intake manifold. Plus, no "check engine", "service" or other light is going off when I'm driving and the car is acting up. The car refused to start yesterday but flooring it when turning the ignition key did the trick (maybe it was flooded due to the too rich mixture?). I then left it alone for a while and the problem solved itself: idle went back to normal, engine coolant gauge gave off normal reading and the acceleration and decelerations were normal.

I drove it to a mechanic friend of mine and he too doubts it's the ECTS again. Could the TPS also make the car rev faster when in gear ? I'll have him check out the throttle body too. It could be dirty.
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Old 07-10-2008, 05:33 PM   #5
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Default Re: SL1 revving way too high at idle and while driving

Read nivlem's post #2 again -- If you can stop the car at the moment the idle is racing, try stopping and re-starting the engine to see if the racing idle goes away. If so, it indicates a bad TPS - Throttle Position Sensor.
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Old 07-10-2008, 05:43 PM   #6
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Default Re: SL1 revving way too high at idle and while driving

Yes, it's after I turned it off (after the motor didn't want to turn over). I then let it be for a while and then the problem magically went away. After wards, every time I stopped the engine, the problem was gone.

My mechanic siad that it only acted on him one time during a 30 minute drive in traffic. I don't know if he stopped the car or not. He'll check it again tomorrow.
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Old 07-10-2008, 05:48 PM   #7
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Default Re: SL1 revving way too high at idle and while driving

The key test is to stop the engine and re-start it right away.
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Old 07-12-2008, 02:01 AM   #8
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Default Re: SL1 revving way too high at idle and while driving

Just a heads up. The car now runs fine again. The mechanic changed the small hose that connects to the PCV: it was very, very frayed and was probably losing vaccum. He also messed around with the IAC, but it looked fine to him.

He was puzzled that the car basically went from dangerous to drive and crazy to smooth by replacing a 3 inches hose... I'll keep an eye open on further problematic signs, but for now, it runs good.

Only annoyance is the tendency of the motor to still have a rough idling, but there's no sudden jumps or anything, just a few sputters now and then (compared to my old Virago '82, that's nothing). Injectors probably need cleaning.
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Old 07-12-2008, 12:00 PM   #9
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Default Re: SL1 revving way too high at idle and while driving

A hole in the PCV hose is a major vacuum leak and the PCM will see the increased air as a lean condition and gleefully add gas. Guess where the RPM goes.

With the antique carburettor such a hose leak would only keep it from running at worst and provide for very hard starting.
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Old 07-13-2008, 12:47 PM   #10
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Default Re: SL1 revving way too high at idle and while driving

yeah vaccum leaks can cause high idle, happened to mine when the vaccum line from the cam cover was dry rotted.
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Old 07-13-2008, 03:54 PM   #11
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Default Re: SL1 revving way too high at idle and while driving

The car is back at it AGAIN.

Car doesn't have any problem starting (hot, since it's damn hot here), but the RPM wil go through the roof (3k) every time. It usually quickly comes back down and will be fine after 3-4 minutes of driving. Turning off the engine and restarting only yields more RPM madness. No service lights or screwy gauges. The car didn't throw any code while it was at the mechanic last week.

This could be the TPS right ? My friend doesn't have a lot of experience working on Saturns, so any pointers I can give him is of great help.

Left caliper also stuck itself to death yesterday evening, leaving me stranded (once again) on the road. The strain of keeping the car in check with the motor racing probably did it in. I had the right one changed this winter when it did this exact same thing (I know they should be changed in pairs, but money was tight).

This car is like an anti-Saturn. Everyone says that checking the oil is the thing that will keep any Saturn on the road. On mine, the motor takes no oil at all. NADA. Zero. It's every other little thing that goes bad
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Old 07-13-2008, 04:21 PM   #12
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Default Re: SL1 revving way too high at idle and while driving

My car use to do the same thing, no codes, & the dealership could not figure it out, I found a posting here, suggesting I check the plug on the tps.
Next chance you get, start the car, pop the hood, and check the wiring on the plug on the TPS by wiggling the wires as the car idles, if the idle changes, you may need to change the connector for the TPS.(this was what worked in my situation)
Also, has anyone suggested that you tap on the TPS while the car idles, if that causes any change in the idle, maybe the tps is bad.


So, yes one can have a bad tps and/or plug for the tps & not have any codes.
Good luck!

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Old 07-13-2008, 04:25 PM   #13
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Default Re: SL1 revving way too high at idle and while driving

Check your fuel pressure regulator, I had the exact same problems on my 96 SC1, pulled the vacuum hose to the FPR and it was dripping with gas, takes about ten minutes to change. I'd also spray some carb cleaner down the IAC port in the throttle body, sometimes they gum up and won't close all the way, but this reeks of FPR.
Hope it helps.

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Old 05-21-2020, 11:34 PM   #14
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Default Re: SL1 revving way too high at idle and while driving

Quote:
Originally Posted by nivlem7 View Post
Would help to know what year the car is. If it's the third generation (years '98-'02), it could be an intake manifold gasket leak. It's fairly common, though the symptom is usually a rough idle. You can find it by spraying some carb cleaner around the intake manifold near cylinder #1. If the idle changes, that's your best bet. IMG failure should also set the Service Engine Soon light. Get the codes read at Advance or Autozone for free, then post the codes here. If it is the IMG, it'll be a P0301 - cylinder 1 misfire detected.

High idle can also be caused by a failing TPS - Throttle Position Sensor, located on the throttle body. Next time the idle is high, try rapping the TPS with a screwdriver handle. If it straightens out, you probably need a new TPS.

You can also try turning the car off and then back on to see if the high idle stays or goes away. Let us know.

Although I've never heard of it happening, the IAC (Idle Air Control) valve could be bad, letting too much air past the throttle at idle.

Only other possibility I can think of is a dirty throttle body. They're super easy to take off and clean.

My manual 02 satun sl with 165700 on the dash idles at 1500 in neutral sometimes after a few minutes of driving was at 2000 before i cleaned out the throttle body and changed the idle air control sensor and if i turn it off and on it fixes itself for a few minutes and then repeats itself. Would appreciate your help! Thanks
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Old 05-22-2020, 12:11 AM   #15
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Default Re: SL1 revving way too high at idle and while driving

I have yet to dive into mine, but I have in intermittent similar problem with my 98 DOHC. Every once in a while, when I put it in neutral or park, it'll idle up to about 1500-2000 RPMs. Sometimes it'll go away within a minute, sometimes it'll do it for several minutes straight. It'll do it if the car is left idling in park as well. Can be sitting idling, and then suddenly jump up in RPMs out of no where. Doesn't matter if it's cool or at full operating temperature. It doesn't miss or sputter, the "idle" is still smooth no matter when it's lower and normal or when it suddenly jumps up. No check engine light, still getting great gas mileage. It's just a very strange happening. It's not enough to where it makes the care dangerous to drive or anything. I don't even notice it when in gear and on the brakes like say at a traffic light. But it does bother me knowing it does it lol.

Going to take a close look at the vacuum hoses first. I might have to try the TPS and plug inspection the next time it starts acting up too. Just have to be ready for it because of how random and sporadic it is...
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Old 05-22-2020, 12:34 PM   #16
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Default Re: SL1 revving way too high at idle and while driving

Quote:
Originally Posted by Cnestlen View Post
My manual 02 satun sl with 165700 on the dash idles at 1500 in neutral sometimes after a few minutes of driving was at 2000 before i cleaned out the throttle body and changed the idle air control sensor and if i turn it off and on it fixes itself for a few minutes and then repeats itself. Would appreciate your help! Thanks
Idle air control valve or throttle position sensor can raise idle rpm. The iacv is pcm controlled to adjust idle rpm in all temperatures from cold startup, warm engine, coasting from speed and when using ac. If it sticks or fails, it can become erratic or stick to one rpm even after cycling the engine off and back on. Think of the iacv as a second throttle except controlled by the pcm. The mechanical throttle plate is controlled by the driver while the iacv is pcm controlled based on sensors.

A worn throttle position sensor sends incorrect signals to the pcm resulting in higher than normal idle. This can be reset by cycling the engine off and back on.

The pcm reads tps signals at startup and memorizes it but a worn sensor skews signals to throw off the pcm, reacting by raising idle higher than normal. Cycling the engine off removes the tps preset. Turning on ignition allows the pcm to relearn tps position to return to normal idle until high idle returns, The tell tale is when restarting returns high idle back to normal idle.
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Old 05-22-2020, 01:23 PM   #17
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Default Re: SL1 revving way too high at idle and while driving

+1 on TPS.

I had same issue, TPS fixed it for a few days, then the symptoms returned.

Exchanged the new defective TPS for another one, then all was good.
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Old 05-23-2020, 10:02 AM   #18
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Default Re: SL1 revving way too high at idle and while driving

Don't discount a sluggish or sticking Idle Air Control. It might be gummed up and not moving every time the computer signals it.

If the IAC was frozen in a single position, the computer would tell you, but the computer doesn't necessarily see a sluggish sensor or actuator as a problem. The software simply looks for changes in readings, so if the actuator sooner or later moves, the computer may see it as "OK". Thus a failing sensor or actuator doesn't always set a code. PLus, the computer has to see a failure more than once in order to set the code. It doesn't see a single odd reading as a failure. To the computer, the component has to fail completely in order to set a code, wherein the computer looks at the actuator or sensor multiple times and gets the same "bad" reading every time.

O2 sensors are famous for not setting codes until total failure. The car may run badly for ages before the sensor fails completely and sets a code. TPS's are another one, and we all know about the infamous ECTS not setting codes.

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