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Old 11-10-2009, 08:28 AM   #1
tad32287
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Default Slow Idle Return

I have been experiencing a problem with the engine returning to an idle or dropping rpms between shifts. If I rev the engine or try to shift the car slowly returns to either the idle or 1500, depending if the car is moving. It's not too much of a problem, but its a hard shift unless I sit with the clutch in and wait for the rpms to drop.
I tried cleaning the throttle body, replaced cracked pcv hose, and cleaned IACV. It worked better for a short drive, and began doing it again. Any idea on a normal problem, or what it could be?

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Old 11-10-2009, 11:28 AM   #2
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Default Re: Slow Idle Return

I am completely stumped. I know when I pulled the pcv cleaned it and put a new hose on it fixed, temporary. I was told that if the piston moves back and forth inside the pcv its still good, as mine does. I sprayed brake cleaner around the throttle body and other hoses to hear for a change in idle and its idles fine at 700. Its just when you rev up the rpm gauge returns to idle slowly, it should be more of a quicker drop. It makes it rough when shifting, you have to hold the clutch and wait for the tach to drop to the right rpms.
Any help would be great!!

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Old 11-10-2009, 01:17 PM   #3
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Default Re: Slow Idle Return

If you rev the engine is place, parked or neutral, and the rpm's return slowly, its most likely a sticky idle air control valve (IACV). The iacv is in the throttle body, (bottom?) and is an electrically driven servo motor that moves in steps to open or close the bypass air port - the hole at the bottom of the throttle bore in front of the throttle plate. Its primary role is to fine tune the idle speed and raises rpm during cold engine starting, warming up, a/c use, and during coasting if a manual transmission is shifted to neutral. The iacv moves in and out to control the supplemental air. If its sticking, the rpm's may not act normally. Removing the throttle body and disassembling the iacv for cleaning should do it - anything to degrease the shaft. Don't allow fluid to drain into the body where the motor resides.

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Old 11-10-2009, 03:39 PM   #4
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Default Re: Slow Idle Return

Yes the IACV is a stepper motor and have tendency to stick. I would take a multimeter and see if you are getting power to it. If you are getting power then I would suggest replacing it. The junkyards would have one for $10 or so, if you want to go new, they run from $45-60 at your local parts store but it would have to possibly be ordered because they don't sell to many of them.

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Old 11-10-2009, 03:56 PM   #5
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Default Re: Slow Idle Return

Quote:
Originally Posted by Ghettoracer View Post
Yes the IACV is a stepper motor and have tendency to stick. I would take a multimeter and see if you are getting power to it. If you are getting power then I would suggest replacing it. The junkyards would have one for $10 or so, if you want to go new, they run from $45-60 at your local parts store but it would have to possibly be ordered because they don't sell to many of them.
You guys are jumping to conclusions on the IAC motor. In as long as I've seen them on all the vehicles I have worked on I've never seen one fail. Doesn't mean they can't but in the last 20 years or so I've worked on an awful lot of them.
OP Change the ETCS and also check wiring. Make sure the throat of idle air bypass is clean and no carbon or oil residue is causing the IAC valve to stick. Check the EGR valve too. Also you may need to reset the IAC motor too. Look up how it's done or do as I do on all the ones I work on. A trick I learned from Chrysler. With the engine idling remove a vacuum line. The engine will speed up. Than cover it with your finger. THe engine should slow way down and nearly die. Repeat. Recennect line and all should be well.

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Old 11-10-2009, 04:27 PM   #6
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Default Re: Slow Idle Return

The "rolling" idle should be about 1400 RPM, so 1500 is only slightly elevated. It shouldn't make shifting harder. If anything, it should help.

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Old 11-10-2009, 05:50 PM   #7
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Default Re: Slow Idle Return

I have the exact same slow return from idle.It drives me nuts

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Old 11-10-2009, 08:50 PM   #8
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Default Re: Slow Idle Return

I cleaned the throttle body up as well as the IATV. Seems to be doing the same. If I unplug the the power to it while running it seems to get a slight better, but not much. Anyway to check to see if EGR is working rather than replacing?

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Old 11-10-2009, 08:57 PM   #9
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Default Re: Slow Idle Return

On what you were saying about resetting the IATV. I used the the inlet to the intake where the pcv hose connects. Just out of curiosity if I hold my finger over the hole without removing shouldn't the car stall out? If so does that mean I have a leak somewhere that would cause the revving/idling problem?

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Old 11-10-2009, 09:40 PM   #10
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Default Re: Slow Idle Return

Misinformation will get you confused associating what someone relates to Chrysler experiences against Saturn procedures proven by members here. Adapting methods without verifying it further clouds troubleshooting.

The idle air control valve (IACV) controls the bypass port hole to adjust idle speed, off-idle speed (coasting), a/c use, and most importantly - cold engine warm-ups. Disconnecting the tps doesn't do anything to prove whether or not it works; its purpose is to tell the pcm throttle position; how does the pcm know throttle position if the tps is disconnected? Leave it connected.

With the engine idling around 800-900 rpm; covering the hole in front of the throttle plate drops engine rpm to 500-600rpm, as mentioned before. This is the factory adjusted minimum rpm set by the throttle stop screw; don't adjust it if the engine doesn't idle at 800-900rpm. Normal idle is 800-900 rpm before blocking the hole. The low idle is the air flowing through the throttle plate - you're blocking the bypass air port at this time and not allowing the iacv to interact with air flow. If you've come this far and the idle holds at 500-600 rpm you can remove your finger from the hole; the unblocked hole now allows supplemental air to increase rpm - blocking it forced the pcm to retract the iacv to attempt raising the rpm but since you stuck your finger over the hole the idle never increases until you remove your finger which now suddenly raises rpm until the pcm detects this. As soon as the rpm rises the pcm commands the iacv to extend its valve to block off the port; the air flow is reduced and returns to 800-900 rpm. All of this confirms an operating idle air control valve. Any other rpm change means; a stuck/broken/faulty iacv.

The tps tells the pcm trottle plate position to correlate all the other sensors to develop the correct fuel/air mixtures. Disconnecting it just confuses the pcm and throws off everything designed to run the engine correctly. Typical tps issues are high idling at random; when the engine is shut off and restarted with the idle returning to normal without touching the gas pedal. The tps is worn out and needs replacement.

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Old 11-11-2009, 08:13 AM   #11
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Default Re: Slow Idle Return

Quote:
Originally Posted by fdryer View Post
Misinformation will get you confused associating what someone relates to Chrysler experiences against Saturn procedures proven by members here. Adapting methods without verifying it further clouds troubleshooting.

The idle air control valve (IACV) controls the bypass port hole to adjust idle speed, off-idle speed (coasting), a/c use, and most importantly - cold engine warm-ups. Disconnecting the tps doesn't do anything to prove whether or not it works; its purpose is to tell the pcm throttle position; how does the pcm know throttle position if the tps is disconnected? Leave it connected.

With the engine idling around 800-900 rpm; covering the hole in front of the throttle plate drops engine rpm to 500-600rpm, as mentioned before. This is the factory adjusted minimum rpm set by the throttle stop screw; don't adjust it if the engine doesn't idle at 800-900rpm. Normal idle is 800-900 rpm before blocking the hole. The low idle is the air flowing through the throttle plate - you're blocking the bypass air port at this time and not allowing the iacv to interact with air flow. If you've come this far and the idle holds at 500-600 rpm you can remove your finger from the hole; the unblocked hole now allows supplemental air to increase rpm - blocking it forced the pcm to retract the iacv to attempt raising the rpm but since you stuck your finger over the hole the idle never increases until you remove your finger which now suddenly raises rpm until the pcm detects this. As soon as the rpm rises the pcm commands the iacv to extend its valve to block off the port; the air flow is reduced and returns to 800-900 rpm. All of this confirms an operating idle air control valve. Any other rpm change means; a stuck/broken/faulty iacv.

The tps tells the pcm trottle plate position to correlate all the other sensors to develop the correct fuel/air mixtures. Disconnecting it just confuses the pcm and throws off everything designed to run the engine correctly. Typical tps issues are high idling at random; when the engine is shut off and restarted with the idle returning to normal without touching the gas pedal. The tps is worn out and needs replacement.
NOt mis-information. Works! I've taught this trick to many GM guys (including SAturn). ALL IAC systems work the same. All this does is close the IAC to it's lowest point and than openit again. This causes the computer to reset the steps for a proper idle. It is the same as using a scanner to reset the steps which is especially handy if one does not have that tool. It does not always have to be done but many times people will remove the IAC and not be careful which moves the pintle. Doing this procedure WORKS and it's fast. SAves people jumping to conclusions and replacing parts for no good reason

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Old 11-11-2009, 11:46 AM   #12
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Default Re: Slow Idle Return

So if the IACV isn't responsible for the slow rpm return, whats next. I heard a mention of EGR but is there a way to test it rather than checking the voltage because that doesn't mean the valve inside is working. Its just strange that when I fixed the leak in the PCV it fixed itself just temporarily.

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Old 11-11-2009, 11:53 AM   #13
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Default Re: Slow Idle Return

As I was researching a little more and picking at my brain, I wonder if I have a restriction in my exhaust somewhere. Although if that was the case, I would notice a difference in acceleration/power while throttling. I am just new to saturns and newer cars in general. I am more of a 70's and back knowledgeable, not so great with emissions.

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Old 11-11-2009, 12:27 PM   #14
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Default Re: Slow Idle Return

My '93 with a 8lb flywheel drops RPM's much faster then my old stock '97 SC2 with the "evil" 18lb flywheel did.

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Old 11-11-2009, 12:51 PM   #15
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Default Re: Slow Idle Return

Quote:
Originally Posted by tad32287 View Post
... I heard a mention of EGR but is there a way to test it rather than checking the voltage because that doesn't mean the valve inside is working....
Have you tried the iacv test? Whether pulling a vacuum line or blocking the port hole in front of the throttle plate? Despite the apples/oranges differences in approaching iacv testing, they're both attempting to force the iacv to retract and extend, not reset, but move to change idle speed. In the end its results you're looking for - whether or not the iacv is adjusting the idle properly. A faulty iacv won't act correctly and can stick to one rpm; remain where it is or raise it and stay high and never return to normal idle. Both tests suggested will demonstrate either a working iacv or not. Sometimes cleaning the throttle is all that's needed to fix a slow idle return.

The egr valve's sole purpose is to lower combustion temps by adding exhaust gases into the intake manifold at the appropriate time during acceleration and cruising. When it sticks or fails it usually creates hesitation, stumbling, balking, and stalling tendencies. The egr valve wouldn't leave the engine with a high idle as it does the opposite; dropping the rpm during acceleration or cruising. Search for egr valve blocking procedures if you're interested in isolating it; blocking off the ports removes the egr valve interaction completely. Those with egr valve failures have seen dramatic results to troubleshoot faulty ones.

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Old 11-11-2009, 01:11 PM   #16
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Default Re: Slow Idle Return

Quote:
Originally Posted by fetchitfido View Post
My '93 with a 8lb flywheel drops RPM's much faster then my old stock '97 SC2 with the "evil" 18lb flywheel did.
+1; I can't help but wonder if this "slow" return isn't just the flywheel effect. I'm also puzzled as to what exactly the "problem" is.

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Old 11-11-2009, 01:40 PM   #17
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Default Re: Slow Idle Return

I did clean the throttle and IACV. I also pulled the line to the PCV and it idled down with my finger over the valve to the intake, and back up when released. I also read about another test where you remain at a idle and turn your AC to max, and or, turn the steering wheel either all the way left or right. If a change the idle was detected then the IACV is working. All of the above worked so I cancelled out that problem.

Someone earlier mentioned the ETCS, and I've heard about it being a problem on a few other forums. Would this affect my problem, or should I just not worry about it right now?

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Old 11-11-2009, 02:02 PM   #18
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Default Re: Slow Idle Return

Knowing you did the iacv test but not posting your results clearly is the only reason I asked to be clear about it. The difference between testing and not posting results just leaves everyone hanging. Replying in text gets it out to everyone reading these threads.

Having the idle stay near 1200 rpm while coasting in neutral at speed is an emissions control program and normal for your car. Prove it to yourself each time by coasting in neutral at any speed above 20mph until the car comes to a stop. The high idle will drop back immediately. The iacv is doing the high idling/normal idling changes. If you can see this occurring repeatedly, there are no problems. High idling above 1500 rpm should be cause for concern and should have been taken care of with throttle cleaning. Normal idling around 800-900 rpm also means no vcauum leaks anywhere.

Review what's been done and see how the engine reacts. To paraphrase, you may be making "much ado about nothing".

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Old 11-11-2009, 10:33 PM   #19
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Default Re: Slow Idle Return

I know Saturns have it set up so that while moving the rpm will stay about 1000-1500. Its the slow return of the idle whether its at 2000 or 5000. It comes back to the idle position of either the 1500 while moving or if I just rev it in neutral, to the 800 rpm idle.

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Old 11-11-2009, 10:36 PM   #20
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Default Re: Slow Idle Return

I had the same problem. Replaced the ECTS and the thermostat and the problem went away. The temp gauge should be between 3/8 to 1/2 when warmed up. The problem with mine did not show up until the weather got cooler. In the summer it was fine. I think the engine was either not getting warm enough, or due to the ECTS the computer didn't think it was getting warm enough.

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