Newish manual driver here

Newish manual driver here.

What does it mean when I'm driving aroun and the car is decelerating, and it sort of bucks back and forth?

Like if i'm decelerating from 4000 rpm in second gear, some times around 2000 rpm the car will sort of jerk back and forth. What is this? While low in the range, the car shouldn't be lugging or anything under the deceleration right? Especially noticeable in traffic.

Also, sometimes when I'm coasting, and I gently apply the throttle (or not) the car will buck the same way when I go to accelerate away.

This happens even if I'm in the powerband, not lugging.

What's happening? Is it bad for the car? I've just been letting it happen.

Car is a 2017 WRX STI

Not enough torque. Probably leaking headgaskets.

Is this bait?

no.. :(

pls enlighten me so i can advance my knowledge of cars a little bit more

See

Shit's fucked. I bet you're around 100k miles and the infamous subaru headgaskets are going.

I've said it before and I'll say it again:
I don't hate Subarus, just Subaru drivers.

Subaru is garbage since they dropped the ej22 desu

The 2006 scion xb I drive does the same thing.

i wouldn't really say i'm a subaru guy.

i only got the sti because the guy at the ford dealership wouldn't let me check what colours he had in stock when I went to buy the RS. i told him i'd give him a deposit, and i didn't even ask for a discount. i was going to buy whatever colour he had. but he didn't even check his computer for what colours he had, he just said that he could show me a focus ST "which was more in my price range".

so i left and bought and sti, i didn't know anything about subarus, but i like the wing.

the car is 4 months old and has 4800km on it

it's a byproduct of the soft bushing and mounts

t. 17 STi owner

>doesn't know a thing about cars
>buys a shitty wrx
Kys

This is NORMAL I can't explain the mechanics behind it so I may be wrong but my car does the same thing. I think it's just drive by wire being fucked, or the ECU changing the fuel rate or something because it is ready for acceleration until it realized you're slowing down, so it isn't sure what to do

ebin trolls

you're a dummy but i'll help. you are letting go of gas too fast, you need to slowly release when at high rpm's

ok thanks! is it bad for the car to do it the jerky way?

it sort of makes me feel sporty.

Why didn't you ask for someone else to help you at the dealership

It's hard on your clutch. Really should use some shitbox to learn on first

Subarus do that. I get bucking from exactly the same situations in my BRZ.

over time you'll learn to be delicate and smooth with he throttle and know just when to press it to avoid them in the first place. perfectly normal with manual gearboxes. you'll end up using your toes for fine throttle adjustments for smoother driving.

are people like you for real?

or do you just ask stupid questions to troll people like me who are easily triggered at the fact that there are people who genuinely wonder why the car jerks back and forth when youre not accelerating.

Do you stay on top of your oil changes? This can sometimes happen when the injectors get clogged up. Once the engine braking process is over and the engine wants to maintain its rpm it need to give some gas, and having clogged injectors can cause jerking.

Also, I can't say because I've never been in your car, but manuals are generally more jerky vehicles. It may be normal and you are overreacting.

Also, you might simply be down shifting too late. Again, I've never driven your car so I can't say, but my VR6 will start shaking while moving at a little below 1k rpm. I down shift at 1.5kish. Try downshifting at a different time and make sure you're rev matching properly.

Don't coast.

It's because the clutch acts as a direct connection between the engine and the rest of the drivetrain and you're not used to that. There is no damping of the power like you would have with a torque converter. If you're not very smooth on and off power with the throttle the car will act a bit jerky, especially in lower gears.

Just learn to be smooth with the throttle. You never want to be stabbing the pedal. Very gently roll on the power until the drive train is torque loaded, it should only take a fraction of a second, then you can punch it.

Idle air control valve might be fucked, had that break on my volvo and it caused massive jerking at 1500 rpm when decelerating

Stability Machine Broke

These. There's nothing wrong with your car, you just need to get used to driving a manual.

It's the calibration mate.
Under acceleration and deceleration the specific fuel delivery requirements of the engine change.
When you depress the throttle the mass of the fuel puddle on the port wall changes and the ecu needs to compensate for this. Its the same as the pump shot on a carb.
When you lift off the throttle the fuel puddle mass changes but there is also likey to be an over run fuel cut in the calibration. If the transition between over run fuel cut and return to normal fueling isn't well defined there can be some bucking as the fuelling demand of the engine isn't being met. Check out x-tau teansient fuelling for more info.

Subarus are very sensitive to changes in air flow. Things that change the air path efficiency (air filters, intercooler, turbo, exhausts, boost leaks etc) will affect the maf calibration which the ecu uses to calculate the quantity of fuel to inject. If you have any of those it may affect your fuelling, or maybe Subaru can't calibrate an engine properly.

Not the car, you just have no fucking clue what you're doing

>all these troll replies
Veeky Forums is clearly fucked
you're probably letting the clutch out too quickly

this.

its driveline slop created because factory bushings are designed with relative comfort in mind. Between loading and unloading the driveline you can have clunks and shit.

Measure flywheel runout.

Problem with boost pressure sensor maybe

He does the exact opposite dummy

Nothing is wrong with your car. You need to be gentle when letting off or going on the gas in lower gears.