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Old 07-14-2022, 11:11 PM   #1
jasenpeters
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1996 SC2
Default Persistent, Intermittent High Idle

1996 SC2 - Complete Engine Rebuild: 2016

In this thread....
http://www.saturnfans.com/forums/sho...d.php?t=237161

I had a similar intermittent High Idle a few years back that either went away or I ignored it, I can't remember. I managed to pass the inspections each year since.

Tends to start and idle fine mostly, then revs high (2k-4k range), and only seems to settle during the same driving trip when coming to a stop.
And that may take a few minutes.

Other days, or even on the same trip when it did idle high, it behaves normally.

Other times, it starts fine, then I go on the highway for about 30 minutes.
I come off the highway and it's rev-ing high per the range stated above.

This has been happening since it started about 3 years ago, I've managed to
compensate my driving behavior to avoid long term high idle.
---

So, now July 2022, inspection time is coming and I decided to give another go at troubleshooting this...
Today:
- I cleaned the IAC. IAC terminals read about 50 ohms per circuit (2).
- I cleaned the TB disc flapper (both sides and edges) and TB intake tubular housing. I did not remove the TB, because I'm not prepared to deal with a gasket...

This is just a preliminary to see if there is improvement.
And there is....but...

It started fine, purred at about 850ish.
The first and only trips so far, the high idle happened, but lower than normal (at the 2k end)
And it began to idle high near the end of the 2 mile trip, as I came out of higher speed (about 40mph).

I'm also superstitious about the weather correlation and the weather was much cooler than normal for ATX, because of an approaching rain storm.

Just looking for ideas on what causes this persistent intermittent higher than normal idle, than can last for more than 1 min with no acceleration pedal being depressed (idle).
Typically, initiates after a long high speed (50-70mph) trip and settles after a long stop.

Previous OBDII Codes thrown were IAC and EGR related.
I cleared the codes since the recent cleaning of IAC.

I would figure these would be a good start to troubleshoot:
- Idle Air Control valve
- Throttle body dirty (flap not closing, linkages dirty, etc...mechanical)

These maybe, but not sure why....as per the symptom: Persistent, intermittent high idle
- Mass Air Flow / Pressure sensor
- Throttle Position Sensor
- Intake Air Temperature Sensor
- Engine Coolant Temperature Sensor
- Knock Sensor
- Crankshaft position sensor
- Vehicle Speed Sensor
- Cruise control circuit (I never use it)

- Hoses
- Positive Crankcase Ventilation valve

- Exhaust Gas Re-circulation valve
- O2 Sensors
- Evap System
- Fuel Pump
- Fuel Injectors

- Spark Plugs, Wires
- Engine Ignition Module

My guess is the high idle is from too much air and would be related to air intake, either a control valve (IAC), EGR (returns air to intake), or a vacuum leak (tube or gasket).
But....I would think that a hose/gasket leak would be more regular and constant.
IAC and EGR's can get stuck intermittently.

Or, a sensor telling the PCM to supply more air or a general command to rev higher for more power to an apparent load.

Just looking for any advice on causes and best approaches toward confirming and repairing the cause.

Thanks in Advance.
...
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Old 07-15-2022, 11:54 AM   #2
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Default Re: Persistent, Intermittent High Idle

It is tough to catch an intermittent problem "in the act"; but if you can, put your thumb over the IAC inlet port to see if the extra air is coming in there. If it isn't, then slide a block of wood/plastic over the TB intake to see if the extra air is getting in there. If blocking the TB intake does not bring down idle significantly, then there must be a vacuum leak somewhere else and there is no point in fussing with the TPS, IAC, TB, live-data, etc.

But, since it may be impossible to catch it acting up, I would guess a leak in either the PCV or brake booster systems; and would try blocking both (one at a time) at their ports on the intake manifold.

The PCV is easy to do, and you can drive like that for many miles/minutes with no harm, but be sure to leave the valve-cover PCV port vented to atmosphere. The brake booster is also easy to do, but braking effort will be much higher than normal, so be aware/prepared for that. You should still have full braking capability, could lock the wheels, but will have to push harder on the brake pedal. You could drive forever with the brake boost disabled, plenty long enough to eliminate that as the suspect...
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Old 07-16-2022, 08:32 AM   #3
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Default Re: Persistent, Intermittent High Idle

Quick test, when it is at the high idle condition, shut the key off (while stopped) for a few seconds and then restart. If the idle returns to normal, replace the TPS. Also look at the TPS connection and see if there is any corrosion. I believe you can get replacement connectors with a short length of wire at Rock auto. Solder and heat shrink is the best method of replacement.
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Old 07-16-2022, 02:29 PM   #4
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Default Re: Persistent, Intermittent High Idle

Same symptoms, as if no change, in the past few days driving.

So cleaning the TB throat and IAC did very little to affect the symptoms.

I'll do the TPS test sometime this weekend.

Thanks all, please keep the ideas coming.
This one is for the books.
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Old 07-16-2022, 05:08 PM   #5
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Default Re: Persistent, Intermittent High Idle

1-No amount of gas pedal pumping will ever inject any fuel into the engine. If you'd like the extensive (geek) technical explanation, I can probably describe it but it may be lengthy and may put anyone to sleep not interested in how EFI systems operate. Sites like https://www.aa1car.com/ can explain EFI systems.

2-While the coolant sensor is brass (replacing the original factory failure prone resin sensor), nothing was mentioned whether or not the two wire connector was/is fouled/damaged.

A quick test when the next high rpm situation occurs; open the hood and flick/jiggle the coolant sensor connector (don't disconnect it) several times and observe any immediate change in rpm.

3-Possible intermittent vacuum leak test. When another unexpected high rpm event occurs, use a quart spray bottle of water to spray every intake manifold port of water, including every vacuum line while bending, flexing, twisting each line to help expose any dry rot damage opening to suck in water resulting in an immediate drop in rpm. Be sure to soak every port and hose with fingers to help expose damage/dry rot.
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Old 07-17-2022, 04:42 PM   #6
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Default Re: Persistent, Intermittent High Idle

Thank you fdryer...

Additional info:

- OBDII Code from reader - P0507 "Idle Air Control System RPM Higher Than Expected"
- Brass ECT Sensor, replaced the resin version about 6 years ago during the rebuild, my model has only the single ECT sensor

I will look into the water spray hose flex inspection, good idea, just tedious.
Not complaining, it will be good experience. Can't grow without a little suffering.

I've begun researching and inspecting the ECT sensor already.
I'll also check the PCV valve.

Thanks All...
...
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Old 07-17-2022, 05:23 PM   #7
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Default Re: Persistent, Intermittent High Idle

Change your throttle position sensor. Use OEM, the aftermarket China ones are garbage.
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Old 07-17-2022, 09:55 PM   #8
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Default Re: Persistent, Intermittent High Idle

Thanks Macgyver....

- PCV value is just the orifice type per OldNuc.... Duralast PCV1009DL, clean as a whistle... was not dirty much, just a little vapour oil residue...

- Inspected the ECT sensor per fdryer, but did not fiddle while idle (sorry) instead, I inspected the leads, gently cleaned the area, the ECT, and the 2-wire clip and wires. Just wiped it down with a soft cloth.

- Did a cursory (not deep) inspection of the vacuum hoses:
- - Brake, Valve cover to intake tube before TB, PCV, EVAP, Fuel Pressure Regulator?, that's all I could see for now...
No visible signs of cracks, breaks or wear....
I will do the water test and report back...

HOWEVER.....
I did a usual test "short trip" for a few miles to get a smoothie, parked, shut off engine, got smoothie, hung out for a few, started up, drove back home.

Good news, is there was no sign of an aggressive desire to idle high the entire time. While moving at say 35mph, in neutral, and coming to a stop the idle dropped to 1700-2200, and gently fell to about 1k at a full stop.
Normally, it would be revving higher even at a stop or in between gear shifting, when it starts to misbehave.

If this is truly an improvement, I'm thinking the fidgeting with the ECT wiring was what did it.

The real test is when I'm on the highway for 30 minutes at 70 and then coming off the highway the idle starts doing its thing and continues on the slower ride to my destination.

I'm still troubleshooting so stay tuned....

As always thanks for the tips and keep 'em coming.....
...
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Old 07-17-2022, 10:15 PM   #9
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Default Re: Persistent, Intermittent High Idle

Some more info, using a OBDII reader
Live data read has....

- ECT sensor reading at 180 to 210 (ish), then the fan comes on
- Temp gauge in car shows a little past half when the fan comes on.

- RPM at idle (not moving) is about 850ish...

I can send other data if needed from the reader if available...
...
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Old 07-21-2022, 11:29 AM   #10
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Default Re: Persistent, Intermittent High Idle

Well....

The local, short trips at lower speeds, have better behaviour with the revving and idle, better but not best (or how it should be).

A few long trips at high speed, the revving was back. Revving high as I came off the highway. The revving persisting after a few stop lights and eventually settling down. But at other times, however less frequent, did not stop revving until I turned off the car.

The only real detectable improvement is it doesn't seem to rev as high (4-5k rpm. now about 2.5-3.5) and the settle down time seemed to be faster.

So I'm thinking, the high speed might somehow be inducing this behaviour.
Maybe the speed sensor....?

It is confusing, but before I go swapping out everything, I'm willing to take
a logical approach.

Something is telling the ECM to rev high erratically or heat is possibly causing
a slow orifice expansion to a vacuum source.

I haven't tested long low speed drives to give time for things to really heat up.
The long high speed trips are up to 1 hour.

Thanks for your patience and advice.
...
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Old 07-21-2022, 11:41 AM   #11
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Default Re: Persistent, Intermittent High Idle

Did you ever try driving it with the PCV and brake-booster ports plugged at the manifold?
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Old 07-21-2022, 09:47 PM   #12
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Default Re: Persistent, Intermittent High Idle

Thanks billr....

Do you mean to disconnect the hoses at the manifold and "plug" the manifold?

How would I plug them? I there a safe and reliable way to do this?
Duck tape?

Once done, then what?
What is the test procedure?
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Old 07-21-2022, 11:33 PM   #13
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Default Re: Persistent, Intermittent High Idle

Yes, disconnect the hoses at the manifold and plug/cap the manifold ports on the manifold. If those ports are nipples, often the easiest way to cap them is to use a very short piece of hose with a plug inside the free end of the hose. Use the unthreaded shank of a screw, a rod, the smooth end of a drill bit, whatever fits nice in the hose. If it is snug, no clamp or tape will be needed, but use a clamp if in doubt. Putting tape (only) over the open end of a nipple will probably not work, as manifold vacuum is strong enough the the tape might get torn and pulled inside. Not a disaster, but would negate the test.

The test is simple: drive the car for a while and see if the symptoms cease or change.

Be careful with the braking! It will take much more foot effort to effect the same braking. Push hard on the pedal, maybe even with both feet, and you can get full braking (wheel lock); but practice a few stops in a non-critical environment before charging into nornal traffic. Are you an avid "tailgater"? You should resist that urge while the brake boost is disabled...

Also, I remind you to leave the valve-cover PCV port open to atmosphere.
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Old 07-22-2022, 08:49 AM   #14
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Default Re: Persistent, Intermittent High Idle

Quote:
Originally Posted by jasenpeters
But at other times, however less frequent, did not stop revving____until I turned off the car.
Quote:
Originally Posted by laser3kw View Post
Quick test, when it is at the high idle condition, shut the key off (while stopped) for a few seconds and then restart. If the idle returns to normal, replace the TPS.
Next time it does the high idle, pull over, shut off the engine, wait 10 seconds, start car back up.
let us know results
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Old 07-24-2022, 03:47 AM   #15
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Default Re: Persistent, Intermittent High Idle

Thanks laser3kw....

After a few high speed (50-70 mph) trips, each at least 15min, the idle began revving higher than the 850 (at stops) and low gear cruising speeds (2k)...
The higher revving was > 2k and < 3k with no foot on the accelerator.

I stopped a number of times during this high idle and turned the car off for
> 10 seconds.

The car, when re-started, was revving high in most if not all cases.

Hope this helps.
...
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Old 07-24-2022, 08:42 AM   #16
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Default Re: Persistent, Intermittent High Idle

If you can, the next time high idling occurs, pull off the road, open the hood and remove the intake air tube to the throttle body and use a finger to block off the port hole just inside the throttle body. You should be able to see it clearly. This is the bypass air port for the idle air control valve controlled by the pcm to adjust all idle rpm from cold starting a cold engine (below 140F coolant temps) thru warmup and when decelerating from speed with throttle closed (many with manual xmissions coasting in neutral notice 1200rpm while coasting until dropping below 10-15 mph).

If you see and hear high idling drop immediately as soon as your finger blocks the bypass air port (suction), this verifies the iacv is commanded to a larger opening by the pcm. This would suggest something is causing the pcm to raise idle rpm.
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Old 07-24-2022, 08:46 AM   #17
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Default Re: Persistent, Intermittent High Idle

Quote:
Originally Posted by jasenpeters View Post
.......
The car, when re-started, was revving high in most if not all cases.

Hope this helps.
Darn! I was really hoping that it would return to normal after shut down and restart.
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Old 08-07-2022, 06:39 PM   #18
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Default Re: Persistent, Intermittent High Idle

And the winner is ..... fdryer !

fdryer's recommendation was what seemed to demonstrate the most notable "cause / effect" connection.

It took a while to do the "finger over pintle port" (FOPP, that's right I'm coining it....) test because the high rev was not frequent enough or predictable for an opportune time to test.

Last night it revved high, no matter how I was driving (fast, slow, etc).
I was determined this morning to forego any further troubleshooting and roll the dice and buy a AZ IACV...$50......but then....

I remembered I had some spare parts I pulled from a SC2 junker I bought years ago when I needed a hood, panels, A/C compressor, etc.
I stripped it clean (I bought it cheap, from someone who drove without oil), and thankfully I had a IACV in the box with other sensors I had pulled.

I cleaned it up, measured the internal resistance on both circuits (~50ohms).
Good match. Short of a bench test, which I don't know how to do for stepper motors (please advise, if anyone knows), I planned for a direct swap.

Before the swap, followed fdryer's instructions, took off the intake air hose to the Throttle Body (TB) and started her up.
First start of the day after the awful high revving the night before.

And, high rev she did. Awesome, now I can try the test.
I have a spare TB and inspected where the fresh air has access to the pintle cavity, just waiting to be sucked in when the pintle opens, so I got a close view of how things are working.
So, I covered the small (~3/8") hole, inside on the bottom of the TB.
This hole leads to the cavity where the pintle opens.
And, sure enough the idle came down to purr like a kitten.

Releasing my finger to open the hole, and back it went to high idle.
A. Pintle is stuck open (internal failure)
B. No electricity to control the pintle (wire harness, connectors, etc.)
C. ECU not sending a signal (connector, ECU circuit)
D. Something is telling the ECU to keep it open (failing sensor)
E. other?
But either way, the FOPP test isolated (affected) the behaviour to the IACV.

Before any tests for wires, ECU, etc. I went for a direct swap with the spare part.
What are the odd 2 IACVs are bad?

Powered up, went straight to idle rpm, and idled like a kitten, no variations.
Took it for a ride....All stops, purr-fect idle....
Took it on the highway, 70mph, between all shifts, idle normal
Came off the highway, back to normal idle....
When shopping....parked it for 20min
Started up....normal idle, went home, same as above in reverse order..
Perfect idle...

Uh.....I think we got it....

So the question is, even though the resistance test on the IACV was good, could it be the mechanism that moves the pintle is damaged so that it can't move the pintle anymore?
And, does anyone know of a bench test to see if the IACV responds properly?

I'm only curious because I want to understand any further detail if someone knows.
It's a labour of love

Regarding fdryer's suggestion:
I'm sure this is a common test, but the simplicity in doing the FOPP test and delivering obvious results is guaranteed, no voodoo, or ambiguity to the process.
For the test, the car runs fine without the intake hose.
Putting your finger over the TB orifice to the pintle chamber does not hurt or burn (with a cold car, of course).
There's no waiting, the idle will change if the pintle is open no matter how slight.
Less air lower idle, more air higher idle.
That simple, in this context, the Idle Air Control valve. Do the FOPP test.

Thanks to the others for their suggestions, as I am now aware of vacuum leak sources, Throttle Position Sensor, PVC and other symptoms.
Thank you for your encouragement and advice.

I will keep you updated if anything changes.
...
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Old 08-08-2022, 09:48 AM   #19
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Default Re: Persistent, Intermittent High Idle

Quote:
Originally Posted by jasenpeters View Post
....So the question is, even though the resistance test on the IACV was good, could it be the mechanism that moves the pintle is damaged so that it can't move the pintle anymore? And, does anyone know of a bench test to see if the IACV responds properly?
If you are sure of iacv pinouts then you can apply 12v momentarily to either coil; one coil extends, the other retracts the pintle valve. One coil fails and the iacv fails; the coil that won't extend or the other coil that won't retract.

Here's a description of iacv function;
https://www.autodaewoospark.com/en/i...trol-valve.php
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Old 08-10-2022, 12:00 AM   #20
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Default Re: Persistent, Intermittent High Idle

Nope, that is not how a stepper works. Both coils have to be energized to drive in either direction, and with specific polarity pattern.

There is no simple way to drive them; and limited way to test the drive signals with only a multimeter. With the IAC connected, back-probe the wires to read voltage across a coil, not a coil lead to ground, You should see about 12V, either + or -, across a coil and it should be changing polarity as the IAC is being driven. Honestly, swapping in a different IAC stepper is probably the most practical test; see if the symptoms change.
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