SaturnFans.com Forums

SaturnFans.com Forums (http://www.saturnfans.com/forums/index.php)
-   S-Series Tech (http://www.saturnfans.com/forums/forumdisplay.php?f=39)
-   -   Sudden idle drop, cleaning EGR & throttle body did not correct. (http://www.saturnfans.com/forums/showthread.php?t=212072)

KSabo 12-11-2015 07:06 PM

Sudden idle drop, cleaning EGR & throttle body did not correct.
 
2002 Saturn SC2 DOHC manual, 186,000.

RPMs are normal for the most part, but when shifting into neutral, idle is dropping to 300 or less, then popping up to 850 as normal or actually dying. Very intermittent but always when warmed up. I took off the EGR and cleaned it and the throttle body last night and this did not correct the issue. Could this be clutch-related? Or?

Thank you in advance.

gveinot 12-12-2015 02:36 PM

Re: Sudden idle drop, cleaning EGR & throttle body did not correct.
 
I had an issue like that but I can't remember if it was my SL2 or my Ford Escort. It ended up being the idle air control solenoid. It was a simple change. The solenoid lets more air in so the engine can maintain load if the AC comes on or you put more electrical load on the car, needing an increase in RPMs while at idle.

KSabo 12-14-2015 07:58 PM

Re: Sudden idle drop, cleaning EGR & throttle body did not correct.
 
I think it is related to the clutch, perhaps not completely disengaging? It happens when I am taking it out of gear and putting it in neutral. Gears aren't slipping though at this point. The clutch only has around 20,000 miles on it.

fdryer 12-14-2015 10:05 PM

Re: Sudden idle drop, cleaning EGR & throttle body did not correct.
 
Correct me if I'm wrong.

1- When shifting from neutral to a gear, the engine isn't engaged to the clutch/xmission so the engine is free revving (neutral) until the clutch is engaged (in gear). Whenever the clutch is disengaged, the engine is free to rev. When the xmission's in neutral the engine is free to rev. No gears are engaged so the entire engine/clutch/xmission input shaft is allowed to run freely.

2-If there's something wrong with hydraulics like a worn slave, master cylinder or leak, gear shifting will not be easy as the clutch is still semi engaged. This would mean the xmission is never fully disconnected from the engine since the clutch isn't completely disengaged. If the xmission is never fully disengaged from the engine, gear shifts will be difficult as the xmission is still turning at engine rpm. This is the classic worn out clutch or hydraulics where difficulty is encountered trying to shift into first gear. The clutch and hydraulics must be in good operating condition to avoid typical end of life situations when either the clutch or hydraulics are worn out.

The EFI system may not be well understood by many, especially when shifting at speed. Emissions control programs and practical engine running prohibits full throttle closure while shifting at any speed. If throttle were allowed to close completely while at any rpm, the engine would starve itself of air and immediately shut down. EFI systems cope with (semi) closed throttle by commanding the idle air control valve to retract and allow air thru and around the throttle plate, supplementing the air flow. This results in a high idle some have noticed when disengaging clutch and either holding clutch down or shifting into neutral and coasting. The high idle, approximately 1200-1500 rpm is programmed to ensure the catcon doesn't cool down. The high idle returns to normal when speed drops below 15 mph. There are circumstances when a worn out, faulty or sticking iacv causes unusual rpm changes.

The easiest way to test iacv function is with a warmed up engine idling at correct (800-900) rpm. With the throttle accessible, use a finger to block the small port in the throttle body (in front of the throttle plate). The rpm should drop immediately down to around 600 rpm. Blocking off the supplemental bypass port where the iacv controls the air flow thru the blocked port only allows air flow thru the semi closed throttle plate. This is the factory setting.

When the bypass air port is blocked, the pcm detected the lower idle and already commanded the iacv to retract completely. Since the port is blocked, nothing occurs until your finger is removed. The moment the port is unblocked the sudden in rush of air raises idle rpm. This sudden extra air flow from the bypass air port allows more air in until the pcm reacts to the sudden rise in rpm by extending the iacv. The drop is rpm back to normal idle is the pcm commanding the iacv to close off part of the passageway until normal rpm is once again established. The iacv reacting quickly is indication of a good one. A sluggish iacv will react slowly. A faulty/broken iacv will act differently from what's described; either stuck in one position with a fixed idle number or raise rpm and not return back to normal idle. The iacv must retract and extend quickly when manually testing its function as described. Simply blocking and unblocking the bypass air port should result in dropped rpm and sudden jump to a higher rpm before returning idle back to normal. The description of the iacv has no effect on clutch use since the xmission is presumed in neutral to allow idling. In normal circumstances, an idling engine doesn't change rpm when shifting in and out of gear while parked (clutch disengaged).

KSabo 12-15-2015 12:28 PM

Re: Sudden idle drop, cleaning EGR & throttle body did not correct.
 
The RPM drop was mainly occurring as I shift from any gear into neutral, as in driving in traffic (1st or 2nd into neutral), when warm. Not from neutral into gear.

Intermittently the RPMs will drop either killing the engine or then pop back up to the normal idle 850 in neutral. It does this 2 or 3 times in a row then stops for unknown reasons, only to happen a day or two later.

This all said, there is a similar behavior this particular car has had since the day I bought it - rarely, when warm and sitting at idle at a stoplight or similar - the RPMs will drop from 850 to 400 or so then pop back up, just once. When I first bought the car new, I took it back to the Saturn dealer repeatedly for this issue and they never could 'find' anything. It's a little obnoxious, but the car doesn't choke out and it is only sitting at idle that it happens every few weeks. So it has been livable. It still does this, though, it did it last night at a stop light.

187,000 miles or so later, we have the new issue of trying to die in traffic when going from in gear into neutral. This is bad news in LA traffic.

The clutch engages right at the floor, and this has been discussed ad nauseum in other threads. It's been this way since installation and may simply need adjustment. I think this is a separate issue from the RPM drop since that just started, but I will go watch a few videos and see if I can adjust the clutch over the holiday break. I will also test the iacv function as fdryer described after work today.

fdryer 12-15-2015 02:01 PM

Re: Sudden idle drop, cleaning EGR & throttle body did not correct.
 
[QUOTE=KSabo;2171285]....The clutch engages right at the floor, and this has been discussed ad nauseum in other threads. It's been this way since installation and may simply need adjustment. I think this is a separate issue from the RPM drop since that just started, but I will go watch a few videos and see if I can adjust the clutch over the holiday break....[/QUOTE]
Well, I don't know of any 'experts' that can state with certainty that hydraulic clutch systems are adjustable because they're not. Either the hydraulics or clutch assembly are worn by the time clutch engagement occurs at floor level. Of course I'm no expert and base my presumptions on basic non adjustable hydraulics and clutch assemblies..............

KSabo 12-15-2015 05:15 PM

Re: Sudden idle drop, cleaning EGR & throttle body did not correct.
 
OK, thank you.

Jmath 12-20-2015 02:09 PM

Re: Sudden idle drop, cleaning EGR & throttle body did not correct.
 
I too have a 2002 SC-2 DOHC Manual almost to 170,000, with seemingly the exact same problem. I just wanted to jump in here since I've been tracking the issue for the past few weeks and I noticed this thread was new.

To be specific, my idle drops very rapidly between gears, enough so that I have to come in heavier on the accelerator to match the engine speed with the next gear. When coming to stop in neutral, the idle will dip down to 500-600 for a few seconds before stabilizing.

Like I said, the I've been tracking the issue for a few weeks without adequate time to change any parts (it has not stalled on me yet but I want to get it fixed over the holidays). I [I]have[/I] noticed that the issue is worse in cold weather. In fact, it completely disappeared for a few days earlier this week when temps were ~60F.

I've run Lucas fuel treatment through it and sprayed carb cleaner through the throttle with it running, with not much change (other than the variance from the outside temps). My plan now is to swap out the idle air control valve.

fdryer, is there a certain IACV that you recommend? I see NAPA has three models (Mileage Plus Fuel @ $41.49, Echlin Fuel System @ $43.49, Delphi Engine Management @ $75.99).

fdryer 12-20-2015 02:50 PM

Re: Sudden idle drop, cleaning EGR & throttle body did not correct.
 
If you can remove and clean the iacv, try this first. You may have a dirty throttle body that may be contributing to issues.

Search around here for testing the iacv (blocking/unblocking the bypass air port while idling). If this test proves the iacv is normal, the iacv isn't the problem. If testing does show a faulty iacv, any replacement can be used. Personally, an iacv is an iacv no matter who makes them.

Jmath 12-27-2015 04:43 PM

Re: Sudden idle drop, cleaning EGR & throttle body did not correct.
 
I took the IACV out, it was caked with carbon. I sprayed carb cleaner through the opening, without taking the throttle body off (it didn't look very easy to do, and I couldn't find a how to or diagram for a 99-02 SC, could only find the SL throttle which is mounted facing horizontally toward the driver side instead of facing vertically like ours).

Then I went ahead and installed a new IACV because I had the part on hand (bought the cheap one) and I only have access to a garage every few months. It completely solved the problem! RPMs are now steady when going into neutral and it revs up perfectly on startup. Thanks for the help.


All times are GMT -4. The time now is 04:48 PM.

Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
SaturnFans.com. The Saturn Enthusiasts Site.