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Old 11-30-2022, 12:48 PM   #1
steve seibel
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Default Problem with engine RPMS falling too slowly when put clutch in-- SL-1

I just posted about a clutch problem (manual transmission), but this is a second, unrelated problem with the same car that's been going on for a long time, maybe over a year.

(1997 Saturn SL-1)

The problem *may* be worse in cold weather, when the engine is cold.

The problem is that when I'm shifting up through the gears, when I take my foot off the accelerator and put the clutch in, the RPM's take an unreasonably long time to fall off. Sometimes they even *rise* slightly, sometimes as much as 200 rpm in the most extreme cases, before slowly falling.

I am careful to take my foot fully off the accelerator *before* I push the clutch pedal in, just to be sure I'm not accidentally revving up the engine, but it doesn't help.

Moving the shift lever into neutral has no effect on anything-- it's definitely not anything to do with the clutch failing to disengage--

Can replicate the problem even while coasting along in neutral, simply by revving the engine up to a higher rpm and then taking foot off accelerator-- again the rpm's take an abnormally long time to fall off.

The problem definitely is affecting my driving--I can't accelerate as fast as I'd like to while merging onto a highway etc, because each time I'm shifting up to the next higher gear, I have to give the rpms a few seconds to fall down to an appropriate level before I engage the clutch again in the new gear--

Any suggestions would be welcome--

Thanks--
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Old 11-30-2022, 12:57 PM   #2
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

I think that throttle response is normal. Both my manual SL2s have been like that as long as I have had them (and one was bought new).

If you can't bang an upshift as fast as you want (like well under a second) then the problem is with the trans syncros; or the clutch isn't releasing fully. I assume you are not double-clutching...
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Old 11-30-2022, 01:06 PM   #3
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

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Originally Posted by billr View Post
I think that throttle response is normal. Both my manual SL2s have been like that as long as I have had them (and one was bought new).

If you can't bang an upshift as fast as you want (like well under a second) then the problem is with the trans syncros; or the clutch isn't releasing fully. I assume you are not double-clutching...
Thanks for the input--

No, I'm not double clutching--

When I say I "can't" upshift is fast as I want, I just mean assuming I want to be "nice" to the clutch and not engage it when I know the engine rpms are still higher than they "ought" to be. In an urgent situation (e.g. merging onto highway in heavy traffic) I still can go ahead and let the clutch out and everything works out fine, I just hate to see the tach needle get dragged down as I let the clutch pedal out because that surely means I'm putting some extra wear on the clutch. I'd rather see the RPM's drop to an appropriate level before letting the clutch pedal back out.

Question: when you say you think you are seeing the same thing-- do you mean even including sometimes seeing a slight *rise* in RPMs immediately after you put the clutch in-- even if your foot came completely off the accelerator before you touched the clutch pedal?

That's the part that just doesn't seem right to me--
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Old 11-30-2022, 01:18 PM   #4
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

"Question: when you say you think you are seeing the same thing-- do you mean even including sometimes seeing a slight *rise* in RPMs immediately after you put the clutch in-- even if your foot came completely off the accelerator before you touched the clutch pedal?"

Yes, that is exactly how mine behave. Don't worry about the clutch slipping briefly at gear change. The two I replaced earlier this year each had over 250K miles, and one was used to teach three children to drive; quite a bit of slipping as they begun.
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Old 11-30-2022, 01:48 PM   #5
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

If you ever tried shifting without the clutch, the RPMs need to be up there anyways to find the sweet spot where the engine RPM is matched to the transmission. This perceived "long time to fall off" is probably by design so the engine RPMs and transmission RPMs are closer.

RPM's shooting up on clutch application though is not normal behavior in my opinion. That can be caused by TPS failure if I recall correctly.
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Old 11-30-2022, 02:44 PM   #6
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

I think the OP is mainly concerned with shifting "up", like from 3rd to 4th. That would require the engine speed to drop as the shift is accomplished. Opposite of what you are describing for a "down" shift (i.e. 4th to 3rd).
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Old 11-30-2022, 04:16 PM   #7
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

The revs hang on purpose. It is for emissions purposes. The actual clutch discs on these seem to last quite a while so I wouldn't worry about that. The biggest issue with the clutches on these in the fingers on the pressure plate seem to take a set after a while.
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Old 11-30-2022, 05:02 PM   #8
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

There is also a several second delay on the dash reading.
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Old 11-30-2022, 10:38 PM   #9
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

Quote:
Originally Posted by billr View Post
I think the OP is mainly concerned with shifting "up", like from 3rd to 4th. That would require the engine speed to drop as the shift is accomplished.
Yes. Like at the shift points I typically use when accelerating, the RPMs need to fall to around 2000 -2200 rpms to avoid any sudden additional drag-down (decrease) when the clutch actually engages. And it takes it several seconds (I dunno, maybe like 4?) to fall down from 3000 rpm or whatever it was running at when I let off the accelerator pedal and pushed the clutch in, down to that number.

I could attach a video of the speed and tach during shifting --if this forum allows vidoes-- but I think the point should be fairly clear if I've explained it well enough--
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Old 11-30-2022, 10:42 PM   #10
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

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Originally Posted by trottida View Post

RPM's shooting up on clutch application though is not normal behavior in my opinion. That can be caused by TPS failure if I recall correctly.
I wish I could nail down *exactly* when I see this *particular* behavior, RPM's actually *rising* a few hundred RPM when I put the clutch in, with foot completely off accelerator pedal.

I think I see it most often when the RPM's are *not* particularly high, like maybe 2000, and the weather is cold and the engine is cold, the latter two items seeming to contribute to quite a high idle . (But still the idle RPM even in these conditions is certainly *lower* than the RPM showing on the tach when I put the clutch in, and see the additional *rise* in RPM.

What does TPS mean? (Throttle position sensor?)
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Old 11-30-2022, 11:04 PM   #11
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

Yes, TPS = Throttle Position Sensor.

I don't think the TPS is bad, though. What you describe, including the few hundred rpm rise, seems quite normal for these cars. Most of us feel no need, in "daily driving", to match the engine rpm to what it will need to be in the new gear; and the clutches last a long time. That has all been said before, I know, sorry to be repetitious.

Last edited by billr; 11-30-2022 at 11:19 PM.
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Old 12-01-2022, 02:23 PM   #12
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

I think you are way over thinking this whole process. Just get in and drive it.
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Old 12-02-2022, 01:04 AM   #13
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

3/4 of the S-Series I've had had crazy rev-hang. Even the 1/4 that were acceptable were still worse than '98-'04 Subaru's. If you're not on the gas pedal and either in neutral or clutch disengaged the engine needs to be at either "stop" idle or "rolling" idle, anything else is wrong. No, shut it. Don't care, it's wrong. No, don't care about that either. Clutch pedal down, off the gas pedal...revs need to drop. Period.

You do eventually get used to it so it's not quite the same bother but if you drive anything else with a manual you'll never get used to it. A 7-8lb flywheel swap helps, but not by enough to be worth the $250+ part cost plus the tear-down effort.
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Old 12-02-2022, 08:43 PM   #14
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

I THINK the rev hang was unique to OBD II cars. Our '95 never did it, and I can't recall ever being in any OBD I car that did. Ours was driven off the dealer lot, so I know it functioned that way stock. Rev drop was immediate with gas pedal lift.

And I'm with Fetchfido on this issue. The revs should connect the throttle position with the exception of rolling idle being ok. I don't want a computer to think for me. Having driven a couple of "rev hangy" cars, I hated it.
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Old 12-02-2022, 10:03 PM   #15
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

It may be worse with the gen2 and 3, but is certainly there with my gen1s.
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Old 12-02-2022, 10:59 PM   #16
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

My 93 SC2 definitely had Rev hang so I don't think it's OBDII only cars.
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Old 12-03-2022, 11:04 PM   #17
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

I wonder why only some of the cars are programmed that way. I know there were a lot of various programs and updates, but our car survived a PCM update with no rev hang.

I remember seeing claims that all years and all S Series had it, and then saw a few comment that certain cars didn't. On ours, regardless of rev range, the revs dropped quickly.
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Old 12-04-2022, 10:19 AM   #18
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Default Re: Problem with engine RPMS falling too slowly when put clutch in-- SL-1

With my 93 SC2, I seem to recall revs would hang for a second when putting the clutch in to shift, then drop fairly quickly until around 1500rpm and pause, and slowly go down from there to idle. It was more obvious the higher the rpm you shifted.

Once warmed up, my 02 SL1 seems to drop rpms fairly quickly but also has a pause around 1300rpm. I've also noticed when coasting to a stop in N, the rpms will stay around 1100 until I come to a complete stop. Once stopped the idle quickly drops to 750rpm idle.

Regardless, seems like normal operation and I never worried about it. Runs fine shifts fine good mpg so who cares.
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