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Engine Revving When Clutch is Depressed Subaru
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youderian
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PostPosted: Sun Aug 09, 2020 6:21 pm    Post subject: Engine Revving When Clutch is Depressed Subaru Reply with quote

I've got a 2.5 Subaru engine in my van and it's acting up, would love any thoughts on troubleshooting.

When the engine is at 2,000-2,500 RPM and I press the clutch to shift the RPMs shoot way up by 1,500-2,000 rpms. I'm not hitting the gas, it's simply a result of engaging the clutch above ~2K RPMs. Super strange.

Any thoughts on why this might be happening? Recently removed the air filter, intake and vacuum hoses to clean things out and re-installed. Double checked and everything appears tight and in place. Using the Kennedy conversion on the 2.5.

Any thoughts are appreciated, thank you!
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PostPosted: Sun Aug 09, 2020 6:38 pm    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

sticky throttle cable?
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PostPosted: Sun Aug 09, 2020 6:54 pm    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Loose motor mounts?

Check them all, then hit Novacafe
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youderian
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PostPosted: Sun Aug 09, 2020 9:05 pm    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Don't think it's a sticky throttle cable as it's actually jumping up on rpms vs. just sticking and only happens at a certain range.
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?Waldo?
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PostPosted: Sun Aug 09, 2020 9:50 pm    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

youderian wrote:
When the engine is at 2,000-2,500 RPM and I press the clutch to shift the RPMs shoot way up by 1,500-2,000 rpms.


I don't understand that statement. 2,000-2,500 is *higher* than 1,500-2,000 but you say the RPMs shoot 'way up'. If the rpms go from 2,000-2,500 to 1,500-2,000 then they either stay the same (2,000 to 2,000) or they drop.
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PostPosted: Mon Aug 10, 2020 5:26 am    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

?Waldo? wrote:
youderian wrote:
When the engine is at 2,000-2,500 RPM and I press the clutch to shift the RPMs shoot way up by 1,500-2,000 rpms.


I don't understand that statement. 2,000-2,500 is *higher* than 1,500-2,000 but you say the RPMs shoot 'way up'. If the rpms go from 2,000-2,500 to 1,500-2,000 then they either stay the same (2,000 to 2,000) or they drop.


I read it 'shoot way up by'.... so that would mean they shoot up to 3500 - 4500, I think....
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?Waldo?
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PostPosted: Mon Aug 10, 2020 6:58 am    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Yes, if he'd said 3,500-4,500 his comments would make sense. The numbers as posted do not make sense to me. If the 1,500-2,000 that he posted is accurate then he should not discount a sticking accelerator cable based on the rpm behavior alone.
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PostPosted: Mon Aug 10, 2020 8:43 am    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

?Waldo? wrote:
Yes, if he'd said 3,500-4,500 his comments would make sense. The numbers as posted do not make sense to me. If the 1,500-2,000 that he posted is accurate then he should not discount a sticking accelerator cable based on the rpm behavior alone.


shoot up by. by means an additional. the rpms jump an additional 1500 to 2000 rpm.

does the OP hear this increase or is it just a faulty reading? how do you know the rpms are increasing? tach or OBDII reading?
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PostPosted: Mon Aug 10, 2020 8:44 am    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Thanks for the thoughts so far.

To clarify the engine will jump up 1,500 rpms if I'm above 2,000 when I depress the clutch. So if I try to shift while at 2,500 rpm, let off the gas and press in the clutch it will jump from 2,500 -> 4,000.

I had ruled out the sticky throttle as if I'm coasting at 2,500rpm and let off the gas it always immediately drops off and I slow down. It's only when I hit the clutch that RPMs shoot up. I'm sure I could be wrong just didn't understand how the sticky throttle cable would be responsible for that situation with the clutch alone.
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youderian
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PostPosted: Mon Aug 10, 2020 8:45 am    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

dabaron wrote:
does the OP hear this increase or is it just a faulty reading? how do you know the rpms are increasing? tach or OBDII reading?


Both. Definitely hear the revving of the engine + can see it on the tach.
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PostPosted: Mon Aug 10, 2020 9:03 am    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Check if your clutch arm is getting caught on your throttle cable sheath. It really should not actually be able to affect the cable, but its worth a look. Is the C clip on the end of the cable sheath at the intake.
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?Waldo?
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PostPosted: Mon Aug 10, 2020 10:36 am    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Thanks for the clarification.
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PostPosted: Mon Aug 10, 2020 10:41 am    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Are you completely lifting off the gas pedal or partially? The TPS is an input for the ECU and maybe it's sending an erroneous signal or the ECU is misinterpreting the signal.

Generally engines have a parameter tuned into them, that cut fuel when the engine rpm is above a certain point and the throttle is closed. You don't notice it, because fuel is readded as you cost down to a stop.
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PostPosted: Mon Aug 10, 2020 12:47 pm    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Yeah, the clutch arm is getting hung up in the linkage somehow.

Get some pictures - there isn't a standard way to do the conversion so who knows what someone cobbled together to get this to work.
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PostPosted: Tue Aug 11, 2020 6:30 pm    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

I know nuthin' 'bout Subies but I thought of you when I read this ad:

https://www.thesamba.com/vw/classifieds/detail.php?id=2378997

Quote:
Last, the engine revs hangs when shifting. I’ve been told this is a peculiar quirk of 2005 Subie engines coming from automatic donor cars like the one in this one. I’ve had several mechanics in Seattle – Peace Vans, Eion’s and NorthWesty – try to diagnose it but we haven’t been able to track it down. I’ve just gotten used to driving it this way.
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PostPosted: Tue Aug 11, 2020 6:36 pm    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Im watching this as my 2.5 converted syncro just started doing this yesterday. Im thinking its a sticky or worn IACV. Will deal with that this week
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youderian
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PostPosted: Fri Aug 28, 2020 1:02 pm    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Solved! The problem was an AC line that I moved when installing a new air filter housing. It got close enough to the throttle cable to rub against it and prevented the cable from releasing quickly and easily once I took my foot off the gas pedal. Easy problem to solve once I spotted it and didn't have anything to do with the clutch. Should have found it sooner.

Thanks everyone who chimed in and hopefully this thread can help someone in the future.
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PostPosted: Fri Aug 28, 2020 3:01 pm    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

Touching is very close indeed. Glad you found your problem and it was an easy fix.
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PostPosted: Tue May 18, 2021 9:35 pm    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

OP here circling back. Started experiencing this same issue AGAIN but this time the AC line rubbing against the throttle was not to blame. And oddly enough it would only happen once the engine was good and hot. Did a couple things to troubleshoot.

First was to completely remove the throttle assembly and all related sensors / valves and clean the assembly. There was a decent amount of gunk in there, so I cleaned everything out with throttle body cleaner and re-installed everything with a new gasket.

Most importantly was removing the Idle Air Control Valve from the throttle body as there was a lot of junk in there. One theory I had was that as the greasy gunk heated up it got stickier and prevented the IA valve from operating / closing properly which allowed more air in at idle, spiking the RPMs way up.

If you're not familiar with the throttle body this video is a great overview of how it works. If you haven't removed / cleaned it before it sounds intimidating but was pretty straightforward to do.

https://www.youtube.com/watch?v=wmrvnZT4aDU

The other thing I did was look for loose hoses for potential vacuum leaks. Found a couple of vacuum hoses in the engine bay that were a little loose and/or didn't have clamps on them. Put some hose clamps over these to ensure my problem wasn't a vacuum leak.

Took it out for an extended test drive today and the problem seems to be gone! Not sure which one of the fixes did the trick but wanted to post in case anyone else is running into this problem and these suggestions may be helpful.
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PostPosted: Wed May 19, 2021 4:47 am    Post subject: Re: Engine Revving When Clutch is Depressed Reply with quote

do you have an fault codes ?
is there a VSS on your conversion.
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