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Discussion Starter #1
I've been driving manual transmission cars ever since 1981. With the exception of the Impreza, it was easy to quickly learn how much to release the gas pedal when shifting out of each gear, in order to reduce the engine RPM to an appropriate value suitable for the next gear. This meant (if done correctly) that the vehicle would not "lurch" (forward or aft) when the clutch pedal was released.

With my Impreza, this appear impossible. Even if the gas pedal is totally released after the clutch pedal is depressed, the engine RPM stays at the prior value for a second before slowly decreasing. Trying to quickly get the engine RPM to a desired value before releasing the clutch pedal, appears to be an exercise in futility. I can only guess that this is for one of two reasons:

  1. Emission control, to avoid a too-rich mixture during a throttle reduction.
  2. Enforced for engine "break-in" for the first 1000 miles (I'm at 820 miles).

I can only hope for #2, because otherwise it appears to be impossible to accelerate rapidly, quickly shift gears, and not avoid a lurch. Otherwise, the only way to avoid the lurch is by letting the clutch out gradually, which is not a great idea when attempting to accelerate rapidly through the gears.

Anyone else notice this? You can also see this effect by pressing the gas pedal when in neutral to give 2000-3000 RPM, and then quickly releasing the gas pedal: the RPM does not fall off immediately.
 

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Yes the rev hang is terrible and unfortunately it is not part of the engine break in. It is 100% for emissions. I?m hoping that a tune shop local to me has the desire based on requests to offer a tune for this car that would eliminate the rev hang. It sucks.
 

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I didn't test drive the manual Impreza but I did test drive a manual Forester and the rev hang was very awkward to me coming from a manual 2005 Legacy.

From research it is definitely emissions related as Buffalo410 said, and Surbau isn't the only company doing it. Seems other manufacturers may be more or less noticeable depending, but the only fix probably is an aftermarket tune.
 

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Discussion Starter #5 (Edited)
What a crock.

I did not buy the manual transmission because I could not stand the Rev Hang.
If I had known this, I probably would not have bought the manual transmission version. During the test drive, I thought it was due to a cold engine.

I suppose that the CVT transmission is designed to deal with this.

What a crock.
 

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Discussion Starter #6
Ongoing research project ...

... From research ... Subaru isn't the only company doing it. Seems other manufacturers may be more or less noticeable depending, but the only fix probably is an aftermarket tune.
I just did a Google search, and it is hard to find a car maker that offers manual transmissions, where this isn't a complaint. There appears to be no really satisfactory solution.

Some dim bulb on another forum recommended "double clutching", not realizing that doesn't help one bit. :grin2: -- "Double clutching" only helps engage the gears, and only works if the engine RPM matches what is needed in the new gear. Since matching the RPM speed is the problem, it's no solution at all.

One possibly useful recommendation is to shift from 1st to 2nd early (before the engine RPM gets too high) to reduce the lurch. That works better with engines that have high torque at low RPM (eg, turbo); not so much with the 2.0i engine in the Impreza.

I suppose the most useful work-around for me is a slower (1/2 second) clutch release. However, I am certainly open to a tuning solution that doesn't affect the biennial emissions test we have to do in Washington state.
 

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I emailed a few tune shops local to me to ask about the options for this car and if the investment would be worth it. So far one got back to me and said they don?t have software for Subaru?s and that tuning a stock vehicle does not produce enough increase to justify the cost. I told him In the original I wasn?t really looking for HP gains more to get rid of rev hang so he must of misunderstood me. Anyways hopefully Monday the rest get back to me and I will share what they say.
 

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Don?t hold your breath. The only engine that has tuners making mods is the turbo XT. No one does tunes on the NA engines. I doubt you?ll find anything different. If you do find someone that wants to hack your ECM, be VERY careful as you can brick it and then you?re really in deep $hit!
 

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I'm strongly considering buying a manual 2018 Impreza, so I'm really curious about this rev-hang issue. Noticed it on 2 different test drives, it was pretty bad. Buffalo410, did you ever find a solution? I can find Youtube videos of rev-hang issues being removed, but they're for older WRX models.
 

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No I haven?t really done any searching since I emailed a few companies and got no results. This is the first MT I?ve had with the rev hang and I really don?t notice it a whole lot. when trying to accelerate and shift quickly it?s a lot more noticeable obviously but I don?t drive like that an awful lot. So I guess it depends how you drive. There are tuning options for older 2.0i Impreza so I think it?s only a matter of time.
 

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I have been driving manual transmission for 15 years and the Subaru is definitely different than your average car. Maybe it is my experience with older Volkswagen cars but the rev-hang is not as much of a problem with some practice.

complete the gear shifting before the clutch pedal is all the way up. Try to find the sweet spot. The Impreza revhangis unforgiving if you don't get it just right. It is hard for me to explain over typing but I spent 2 entire days practicing fast accelerations until I started to get the hang of the sweet spot. It is still annoying but anything beats the CVT.

I will add I have the sport model with STI short throw shifter, but I did test drive a base model.

I will also add if anyone knows a tuner that can get rid of the rev hang let me know, because rev hang is the devil.
 

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I have been driving manual transmission for 15 years and the Subaru is definitely different than your average car. Maybe it is my experience with older Volkswagen cars but the rev-hang is not as much of a problem with some practice.

complete the gear shifting before the clutch pedal is all the way up. Try to find the sweet spot. The Impreza revhangis unforgiving if you don't get it just right. It is hard for me to explain over typing but I spent 2 entire days practicing fast accelerations until I started to get the hang of the sweet spot. It is still annoying but anything beats the CVT.

I will add I have the sport model with STI short throw shifter, but I did test drive a base model.

I will also add if anyone knows a tuner that can get rid of the rev hang let me know, because rev hang is the devil.
Back in the old days the “rev hang” was caused by a mechanical dashpot, one of the first things (among many) that got removed from my 1976 BMW 2002 engine bay. I’m sure it’s all electronically controlled, so no easy fix.
 

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Back in the old days the “rev hang” was caused by a mechanical dashpot, one of the first things (among many) that got removed from my 1976 BMW 2002 engine bay. I’m sure it’s all electronically controlled, so no easy fix.
The fact that it's electronically controlled makes it even easier to fix ... in theory. It's just a parameter in the ECU (Engine Control Unit a.k.a. 'computer') The problem is that nobody has reverse engineered the software used in the current generation of non-turbo Imprezas.

There have been a lot of people with a lot of motivation to figure out the WRX unit, so it's been done, at least the older ones. With free, open source software you can adjust every imaginable detail of engine control. But the motivation just isn't there to figure out the non-turbo FB engine computer, so they remain mostly a mystery. Too bad.
 

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rev hang

everyone is correct on the cause of the rev hang..here are some other observations.

i have a gps unit that plugs into the obd and brings up 10 different engine functions as the car drives..

when the car is put into gear at a stop the engine timing changes... what the **** are they thinking..
i have driven stick shifts and only owned stick shifts since i was 16. thats 49 years.. never have i had the shifter affect the timing..
it changes 2-3 degrees..totally crazy

this car is set up to be fuel starved...i noticed when its 10 degrees outside for example and the car is cold there is no rev hang the car runs like a champ. as long as it really cold and the ecu tells the engine it needs fuel ie:choke on the car runs as we know a stick shift should run..

like everyone else who has driven stick shifts for years this car is hard to shift smoothly between first and second. love getting back in my 09 legacy such a pleasure to shift..

they will make a lot of subaru owners with stick shifts happy when they come out with a fix.
 

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There are a couple of transmission harness connectors accessible from under the air intake. One (dark gray) tells the car to turn on the backup camera when in reverse. That one should stay connected. The red one? Not sure what the car does with the manual transmission position info from that one. The gear position indicator seems to still work. I'm going to leave it disconnected for a bit to see what changes. IMAG3107_1520797450929.jpg
 

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I'm not sure if it's a placebo effect, but I think this may have reduced rev hang. It seems like when I go from 1st to 2nd now, that the revs can drop normally under initial clutch load. Before, it seemed like the car would keep the revs high even as the clutch was engaging.
 

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This is the harness I disconnected one side of:

https://www.subarupartsoutlet.com/a...9220/MT--TRANSMISSION-HARNESS/G14-119-01.html

I wrapped my loose connectors up in self-fusing silicone tape and zip tied the pigtail end in place just to be a little bit neat about it. I don't foresee ever connecting them together again though. The revs seem to behave now how they would on a typical fuel injected car. Not quite as satisfying as a well carbureted car, but not artificially slow to drop anymore.
 

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I am extremely interested in your findings! Are you getting any warning lights or check engine lights with the sensor disconnected
 

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Everything seems to work fine, including gear indicator on the dash. No warning lights, speedometer is fine, etc. No negative effects that I can find.
 

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I really want to try this. Not that I doubt you but I always wait for a second person to try before I risk it. I'm hoping a second person also confirms your findings soon, both that it helps and that there are no consequences. I am also very curious on what the sensor you disconnected is actually for.
 
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