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Discussion Starter #1
Hello All,

I recently purchased my first WRX - a brand new 2020 base model. Overall, I love the car. But I've been experiencing an intermediate issue that is driving me absolutely nuts. I'm hoping that someone here may be able to enlighten me about the cause.

The issue appears like this:

I'm completely stopped at a stop sign, preparing to turn right. Vehicle is in 1st gear and clutch is pressed to the floor. Because of the geometry of the intersection and limited visibility, I have to lean into the intersection just a little bit with my wheels slightly turned to the right. Traffic is clear, so I go to take off.

I start to release the clutch and give it a little gas as normal. But instead of accelerating normally, the throttle response is substantially weaker. Suddenly there is a pulsating feedback. Not a violent shudder, but a notable sensation pulsing several times per second, similar to the sensation of ABS kicking in. The Hill Assist light suddenly appears on the dash and the engine quickly stalls. All of this happens in the span of 1-2 seconds.

So I press the clutch back to the floor, restart the engine and try to accelerate again. Same phenomenon. Reduced throttle, pulsating feedback, Hill Assist light, stall.

Once more I restart the car. This time I rev the engine to 2,000 - 2,500 rpm and release the clutch extremely slowly. The vehicle struggles to move forward but manages to get moving without stalling. However, something is still very wrong. Throttle response is still extremely week. Pedal is nearly to the floor, but vehicle accelerates at a snail's pace, and the engine RPM's refuse to climb. The pulsating continues for another 20 feet or so. And the Hill Assist light is still on.

After about 100 feet, I've finally gotten the vehicle up to speed. So I press the clutch and shift into 2nd gear. I release the clutch, and all of a sudden the engine RPM's shoot up to where they would normally be at that speed in that gear. The Hill Assist light goes off and the vehicle behaves perfectly normally from there on out.

I've owned my WRX for about 3 months now and I've experienced this issue 3 times. What's really perplexing is that every time I've experienced this issue, it's been at the very same stop sign! There's nothing particularly noteworthy about this intersection. Nearly flat with clean, dry pavement.

Am I doing something wrong here? Granted, this is the first manual transmission vehicle that I've owned. But I've driven others in the past so it didn't take me long to get smooth at driving my WRX. And (this issue aside) I haven't stalled it since my first week of ownership. So if it is something that I'm doing wrong, I can't image what.

Is it possible that the Traction Control System is erroneously kicking in and applying the brakes (causing the pulsating sensation) and limiting the throttle? I can't imagine why TCS would kick in under gentle acceleration on clean, dry pavement and then persist for 100 feet for or so until I shift into 2nd gear.

Could it be a faulty wheel speed sensor engaging the TCS? Seems unlikely on a brand new vehicle. And it doesn't explain why it only happens at one specific intersection.

Could it be a faulty incline sensor causing the Hill Assist to fail to release the brakes? Again, unlikely on a brand new vehicle. It doesn't explain the reduced throttle response. And I regularly take off from a stop on much steeper hills without any issue.


TL;DR:

When gently accelerating from a stop on a relatively flat surface, vehicle experiences substantially reduced throttle response, pulsating feedback that feels similar to ABS, Hill Assist light appears on the dashboard, and vehicle stalls. Intermittent issue - has happened 3 times in 3 months at the same intersection.


So I'm at a loss...

Any thoughts on what might be happening here? Any insight is greatly appreciated.

Thanks.
 

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This might not be the answer your looking for but I’ve owned many WRX over the years. Grab a cobb access port reach out to one of the many E-tuners and get a stage 0 tune on the car. No physical modifications needed.

you literally won’t recognize the car it’ll be faster, more fuel efficient to a point and all the stupid Subaru factory issues can be resolved with a tuner.

my 2017 wrx stuttered on the way out of the dealer. 2500-3k Rpm it would stutter like if it was running out of fuel on a full tank lol. Spoke to a tuner and fixed it. The factory software on these cars are horrible.
 

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Discussion Starter #3
Shinte122305,

Thanks for the suggestion. I've only had my WRX three months now, so I'm not quite ready to change the tuning just yet. But when I am, I will definitely keep that in mind. Is there any downside to the stage 0 tune? Do you happen to know if using an e-tuner will void Subaru's warranty (silly question probably, but the vehicle is still new)?

To clarify the issue I'm experiencing, it's definitely something far beyond a little throttle or turbo lag. When this issue hits, it takes me 100 feet or more to accelerate to 10 mph. The whole time, engine rpms remain extremely low (even though I have moderate throttle applied), there's a pulsation through the drive train that feels like ABS activating (even though I'm not on the brakes), and the Hill Assist light remains lit (even though I'm on flat ground and moving).

It really feels like the Vehicle Dynamics Control (VDC) is kicking in, which cuts throttle input and selectively applies the brakes. But I can't prove it. And I can't imagine why VDC would activate during very light acceleration through a gentle turn into a straightaway on clean, dry pavement. Or why it would stay activated for so long. I also don't recall the TCS/VDC light appearing on the dash (but each time, it all happened so fast).


Two small updates:

First, I borrowed two different OBDII readers from some coworkers. Neither showed any codes. But neither reader was a super high-end model, so they may not have been accessing all areas of the vehicle. I plan on buying a more comprehensive OBDII reader to see if that shows anything different.

Second, I've started driving through the problematic intersection with TCS turned off. Of course, this is not any kind of long-term solution. But my thinking is that if I drive it for awhile with TCS turned off, and I don't experience this issue anymore, that seems to indicate that the issue is somehow related to the TCS/VDC system activating inappropriately. Hopefully someone here will let me know if that logic does or does not stand up.


Still not sure what is going on here. If anyone has any other ideas, I'd love to hear them. I'll post updates if and when I learn anything new.
 

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In my honest opinion If the car is 3 months old please take it back to Subaru and make sure you let them know that your in danger when turning into traffic because the car stalls out. They will cover it completely since the car is new, stop wasting time tinkering you never know if it’ll happen with some guy speeding behind you and then your really screwed.

on a side note when you get that resolved with the dealer, buy the cobb access port lol. Do not use any of their tunes after buying it speak to an E-tuner and let him know you want a stage 0 tune no mods. When you do all that with him you’ll fall in love with your car. There is no downside to a stage 0 if you need to go to Subaru for something you can simply plug in the access port and remove the tune completely back to factory I’ve done it a million times and so has everyone I know.

the real issue is physical mods because at that point you'll need to remove those and the tune lol. But these new FA20 motors really come alive with a tune. I HATE the factory tune your literally giving it 80% power at 50% throttle lol it’s so bad.
 

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Discussion Starter #5
Shinte122305,

I fully agree - I have an appointment with Subaru for Thursday. I just know that these intermittent issues can be a real PITA to track down. Of course, they never appear when the service tech test drives it. So I wanted to do a little homework first to see what I could learn. I was hoping somewhere here might have said, "Oh yeah, I've had that same issue. Here's exactly what it is." Or alternatively, "You're still relatively new to driving stick, so you're probably doing this by mistake." But it seems like neither is the case.

We'll see what Subaru says. Maybe I'll get lucky and they'll have a service bulletin out for this issue.

Thanks for all the info about the stage 0 tune. Once I get a little more experience with the car, it is definitely something I'll look into.
 

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Well, I got the car back from the dealership yesterday. No surprise - there were no error codes and they were not able to replicate the problem. They said they drove it around their automotive complex, started it off on a hill, and even intentionally stalled it. And the issue did not appear.

And wouldn't you know it - the issue appeared for me on my drive in to work this morning - same exact intersection, same symptoms. The only difference was that this time I recognized the issue instantly, so I nailed the clutch before the car could stall. There was the slight scent of (what I assume was) burnt clutch (even though I hadn't slipped the clutch at all).

So I pulled the shifter out of first gear and then popped it back in. The car then took off normally, and continued to operate normally for the remainder of my drive to work. A drive which includes a number of red lights and hills - so plenty of opportunities to try and recreate the problem. Yet the problem did not reappear.

It may be worth nothing that this morning I was driving it with the TCS turned off, so I think that eliminates TCS/VDC as the source of the problem.

So I'm now rolling over two new theories in my head:

1. For some reason, the car is not getting fully into first gear. My vehicle came with the "Short-Throw STi" shifter. Is it possible that something there is a little loose or not properly adjusted? From my end, it sure feels like the shifter is locked into position when the issue occurs. But maybe internally the linkage is not quite getting the gear fully engaged. I've tried a few times to intentionally put the car "halfway" into first gear to see if I can replicate the problem. But I have not been successful. The shifter either locks into gear or pops back into neutral. There is no "halfway".

2. Is temperature playing a role? Each time I've encountered the issue, it's been on a rather cold day. That also might explain why it always happens at the same intersection. That intersection is only a mile or two from my home. Maybe that distance provides just enough time for some components to start to warm up while others remain cold. Perhaps that temperature delta is causing the issue.

Again, I'm at a complete loss here (as is the dealership). Has anyone else out there encountered anything like this? Does anyone have any ideas what might be going on here?

Thanks in advance.
 

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Discussion Starter #8
One more theory: Hill Assist is failing to disengage.

After a little more searching on the web, I've found a number of people complaining that their Hill Assist was sticking (mostly Forester owners, but I imagine it's the same system on the WRX).

That would make sense. It felt to me like the throttle input was being reduced, but maybe the engine was trying to produce power, but was struggling to fight the brakes. That would also explain the smell (burning clutch and/or brakes).

It would also explain why it is specific to one location. The particular intersection where the issue occurs is on a slight uphill grade.

Cold may still be a factor. The issue has only appeared at the beginning of my commute on cold days. Maybe the incline sensor is acting up due to the cold, or the brakes are mechanically failing to disengage.

Any thoughts?

I think my next step is going to be to drive with Hill Assist turned off for some time and see if the issue disappears. Not a long term solution, of course. On a brand new car, Hill Assist should be expected to work normally. But this may help me to pinpoint the issue.
 

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I have never used hill assist, honestly that’s for people who don’t know how to drive stick well. Me and all my friends drive stick without it with no issues ever. If you learn your car well you’ll never want any of that stuff just use hand brakes as your manual hill assist to learn your car.

by everything your saying it does sound like the brakes are being applied.the smell shouldn’t be clutch unless you were riding the clutch I don’t see why you would smell it. The few times I’ve smelled it in my wrx was from a hard launch that I did stupidly lol.
Another thing have your psi gauge open on the dash. Even if you think the engines struggling you’ll see the gauge that shows the motors psi and % of throttle.
 

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Also, grab a dash cam or something and record it. If you can record it the dealership has no choice but to find the issue lol. Plus it can help others online. I can’t tell you how many times I’ve tried to help people here and when they show the video I instantly figure it out and realize everything we have said is wrong.
 

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Discussion Starter #11
Shinte122305,

Thanks - that is a really good idea about watching the digital boost and throttle gauges. I'll make sure I have that screen pulled up next time. And I've been wanting to get a dashcam anyway, so this is all the more reason.

Full disclosure - I would say that I'm still relatively new at driving stick. But it didn't take me long to get smooth with the car, and I definitely don't slip the clutch under normal driving conditions. And (this issue aside) I haven't stalled the car since my second week of owning it.

All that being said, it's probably a good idea for me to get comfortable using the parking brake on steep hills anyway. Not all cars will have Hill Assist, so I'd rather learn to rely on my skill level rather than the automated features of the car (which apparently do not always work as intended).
 

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I’ve never seen a hill assist work as smooth as a skilled driver. I’m no pro but I’ve been driving stick for 20 years. All my friends and coworkers call me to drive their new baby home lmao.

Just practice with the hand brake, the worst that can happen with that is you either hold the handbrake too hard and you might stall out so you need to quickly press the clutch in and reset or you do it too late and start slightly falling back either way I’d reccomend going really early in the morning or late at night to practice before doing it in traffic.
It’s easier than it sounds on like your 5th attempt you’ll be a pro lmao
 

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This same things has happened to me since I got my 2016 WRX but only on a sharp inclined turn at slow speed. Funny thing, by wife has a dual-clutch in her car and it does the same thing. Definitely turn off hill assist and take the turn as wide as possible from a stop or near stop.
 
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