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Engine lugging(?) at above 2500rpm

57K views 197 replies 55 participants last post by  Octal450 
#1 ·
Hi everyone, new to the forum, and a new Subaru owner. Just picked up a 2018 Impreza Sport in manual last Monday. I've really been enjoying it so far and I have about ~700 miles on it. I know I'm still in the break in period but I've been having a kind of wierd issue, I don't know if I should take it back to the dealership or something, this is also my first brand new car. It seems like in second and third gear specifically, but sometime fourth, I'll get what kind of feels like the engine lugging, but all the way up to 4000 rpm. It's hard to explain it but I would say its similar to accelerating on a motorcycle that has a dirty carburetor. It accelerates, then almost like, skips for a second? It just makes for an overall un-smooth acceleration and I'm wondering if maybe I have something wrong? Should I bring it back, or maybe just try higher octane fuel?

Thanks in advance for any help you can provide.
 
#2 · (Edited)
Welcome!

I was told when I bought the car that the ECU has to go through a "learning" period. The car has to learn many things and learn your driving style as well. I know this sounds strange. My dealer told me to do "jack rabbit" starts as much as I could (but not to redline it) for the first month of ownership.
 
#3 ·
Welcome!

I was told when I bought the car that the ECU has to go through a "leaning" period. The car has to learn many things and learn your driving style as well. I know this sounds strange. My dealer told me to do "jack rabbit" starts as much as I could (but not to redline it) for the first month of ownership.
Yeah I guess I can see that, I had assumed that since I was within the break in period it could just be that. I do notice that it only feels not smooth when I'm accelerating lightly, if I floor it the power comes on smooth.
 
#4 ·
I have a CVT and during my break in period I experienced some "stuttering" at low speeds around 1000-1500rpm. Similar to CJ I was also told this was normal and part of the "learning" process. I just broke 6,000 miles and that issue isn't an issue anymore. I can't speak for manual, but I'm sure it will dissipate as you drive it more.

Thanks for joining the forum!
 
#5 ·
Thanks, I appreciate the response! I guess I'll just keep driving for a while and see how she goes. I think I still may just be readjusting to driving a car with a manual transmission, although I'm sure all this Boston traffic will strengthen my left leg quickly! :laugh:
 
#6 ·
There are a few of us....all with manual transmissions with this problem. I've had it to the dealer 3 times about it and even called subaru of America and gotten no satisfaction. They all say its "normal operation". It's so frustrating sometimes that I'm probably going to get rid of the car as soon as financially possible. It's gotten to the point of being dangerous a few times (ie. Even downshifting on a hill won't gain me any acceleration and I end up doing 35-40 on a 55mph road)
 
#7 ·
I'm coming up on 12xxx on my manual trans Impreza, and I don't recall this ever being an issue. I drove it like a granny for the break-in period, keeping it at 3000rpm and below. 3000rpm in 5th is a pretty reasonable speed though. After 5k or 6k, I did notice the engine power increase. But I've never been unable to find a gear for the acceleration I wanted, after I got through the break-in period. Being good during the BiP really sucked.
 
#8 ·
I do not know if Subaru does this... but some automakers program into the computer to PREVENT excessive RPMs during break-in period. Is it possible that the computer is simply preventing overrevving above 2500 RPM until some preset miles is met?


Perhaps someone with manual xmission who has over ...say 2000 miles is experiencing this issue?
 
#12 ·
So, I'm seriously considering going to my local dealer and showing them this thread, and the other one that illustrates this issue. They and SOA have been thus far unwilling to do anything about it, but I'm wondering if enough of us bring it to their attention if we can get them to do something.

I've narrowed it down to either a software/programming issue or something heating up and causing the computer to overcompensate. My car seems to do it more after an hour plus driving.... and then it will continue for a day or two after until whatever is causing it "resets" for lack of a better explanation, at which point it drives normally for an undetermined amount of time before doing it again.
 
#15 ·
Same symptoms on my 2018 Crosstrek (same engine). Started happening sporatically but now doing it all the time between 2-3k rpm.

I emptied a bottle of Techron fuel injector cleaner into my tank this morning on the theory that the DI injectors in these cars are prone to fouling from using non-top tier brand gas. Take a look at what the direct injector's in this guy's FA20 engine look like after 17k miles. He had the same symptoms, dealer fixed by replacing injectors.

Edit: can't post the link to the thread, but you can find the photos by googling "ft86 engine bogging / stumble"
 
#16 ·
I emptied a bottle of Techron fuel injector cleaner into my tank this morning on the theory that the DI injectors in these cars are prone to fouling from using non-top tier brand gas. Take a look at what the direct injector's in this guy's FA20 engine look like after 17k miles. He had the same symptoms, dealer fixed by replacing injectors.

For future reference:
Due to direct-injection into the combustion-chambers, anything you put into the gastank will NEVER touch the back of the valves where the crud collects.


The ONLY way for a 'cleaner' to get to the back of the valves would be to feed it into the intake-manifold.
 
#24 ·
Fuel system cleaners are scammy in general. And if you have less than, say, 50k on the odometer, there’s no way the injectors are clogged unless you’ve been using really bad gas, in which case you would have noticed other issues with misfires, knocking, etc.

Post #2 is probably on the mark, IMO. There is a learning period where the ECU will adjust air/fuel ratio based on O2 sensor readings over a period of time.

If you floor it (wide open throttle, or WOT), the ECU will shift to “open-loop” mode, where it basically ignores the O2 sensor. If you feel the engine is lugging, floor it and see if there’s a change.

If not, something else is wrong, and as others have noted, it may need to be brought to SOA’s attention.
 
#26 ·
I can tell you it's not the ECU learning. Like I said theres several of us with this issue in here. I contacted SOA and had it to the dealer 2 times for the issue and they all say "normal operation". Which is code for "yeah theres something wrong but we dont wanna spend the money to figure it out".
 
#31 ·
Yeah like I said, I'll see if I notice a difference with the AC off, couldn't test today as we're in a heat wave lol

Have you switched different gas locations with tier 1 gas?
I don't think I've noticed a difference between gas stations, but I typically always get gas at Cumberland Farms so I can get the extra 10c off per gallon.

I was considering going to a station down the street next time that sells ethanol free gas (supposedly) and see if I can tell a difference there.

Kind of worried I might confuse the ECU more by changing so many things in succession though with only about 1400 miles logged.
 
#32 ·
Doubtful it's the AC, as I have not seen any correlation.

Your experience with the fuel injector cleaner mirrors mine - problem came back shortly after.
Same thing higher octane gas - short term improvement, but issue eventually returns.

My current theory is spark knock caused by carbon buildup in the valves or upper cylinder.
Today I ran a bottle of Seafoam through an intake vacuum hose. Tons of white smoke.
Hoping this provides a longer term remedy. Time will tell.
 
#34 ·
2018 manual impreza loss of acceleration

I have a 2018 impreza wagon, manual transmission. I have 23,000 miles on it. I drive 1200 miles a week to and from work. Since about 18,000 miles, in gears 2-5 at 2500 rpms it stutters and doesnt fully accelerate. It's been in the shop 4 times now and no one can figure it out. Super frustrating!
 
#35 ·
Folks, my confidence is increasing that this issue is caused by carbon buildup on the intake valves.

For those suffering from this issue, I highly recommend running a bottle of either Seafoam (get the one that comes in a spray can) or CRC GDI intake cleaner through the vacuum hose on top of the intake manifold. Make sure the engine is warm before applying the spray, then shut off the engine after depleting the can and let it heat soak for 30 minutes before restarting and flushing out the smoke.

Alternatively, Subaru has their own product called Upper Engine Cleaner that the dealers can perform but since it doesn't come in a spray can, I believe it requires a special hose to apply.

After doing the Seafoam, I had a noticeable improvement in power delivery under load - the engine responds and accelerates exactly as expected to pedal position, and the 2500rpm stumble (which I would get several times on average on my daily commute) is gone.
 
#36 ·
Alright so a continuing development on this issue. Drove about ~500 mile total over the last weekend and the stuttering and lack of acceleration has still been an issue. Filled my tank with 93 a few times thinking that might help, but nothing. Highway driving has kinda sucked as while I'm on 5th gear at 65, most of the time if I hit the gas I'll either not accelerate at all, or I'll actually SLOW DOWN, which really sucks, I'm at around 2700RPM which I know isn't where it has the most power, but even my 2001 Kia Rio never slowed down when I put the pedal to the floor.

Seems to be less of an issue if I have the AC off, but as we've been experiencing a heat wave on the East Coast that's been kind of a no-go.

Just scheduled an appointment with the dealership for tomorrow afternoon, I'll update if they are able to do anything.
 
#37 ·
Dealer said basically exactly what I thought they would say. "THE VEHICLE IS OPERATING AS INTENDED" They said they would test drive it, but I'm doubting they did at this point considering they only had it for about 30mins, the nearest highway is easily a 15 - 20min drive with traffic around here and I said it was a highway speed issue mostly. Also they said I came in with 2230 miles and left with 2238, but my odometer was at 2233 when I left.

So basically they wasted my time, tried to explain to me how gearing in a transmission works (like I'm some kind of moron) and said it was just how 5th gear works.

Has anyone had this issue an resolved it with an intake kit? I'm almost certain it's an air/fuel ratio problem
 
#45 ·
Seems to be working still. Every now and then it's a little inconsistent in acceleration (starts out weaker than usual, then power gradually comes), but I no longer get any completely dead spots where the car won't accelerate at all.

However, on pretty much every trip, I still get audible spark knock (sounds like the popping noise of a Geiger counter) when barely touching the throttle. Car drives fine otherwise.
 
#47 ·
Just the one-time Seafoam. I had a scangauge monitoring all sorts of things - A/F ratio didn't show anything odd. stft and ltft were within spec. On hot days, knocking correction degrees and the so-called "roughness monitor" did go up periodically during acceleration, but this data wasn't very helpful because scangauge doesn't have a way to log the data, and I didn't have any known "good" measures to compare against. Anyhow, Seafoam shouldn't be used too frequently - before an oil change is best.

For me though, between the pinging, the rev-hang, the transmission whine, and my uncertainty over the long-term effects of carbon buildup and durability of these high-compression DI engines, I likely won't be keeping the car for too much longer.
 
#48 ·
Yeah I actually finally figured out how to get a few more parameters up in Torque Pro, I'm not a mechanic or anything so I'm not sure if what I'm looking at is good or bad really, but what I did notice was when the car was accelerating smoothly the timings had advanced to like 20 degrees or so, however once I got to around 2500 rpm where I was having issues the timings would retard back to like, -3 degrees or something. I feel like this maybe is an issue somehow? Air Fuel ratio didn't drop either while this was happening, although I was trying my best not to focus on my phone screen while I was driving.
 
#49 · (Edited)
For context here's a screenshot from Torque showing my recorded air/fuel ratios and engine timings, the markers denote the min and max for the session, this was over about a 2.5 mile drive home from work, as you can see the engine timings seem to go pretty far into the negative, is this right? I can't seem to find anywhere where negative engine timings are correct?
 
#51 · (Edited)
Can you guys run a tank of premium and see if it's still pulling timing? I'm curious.

Edit (why I'm curious):

The Impreza has a very high 12.5:1 compression ratio. Direct injection does have a charge cooling effect so let's conservatively say it'll combust like a 10.5:1. That's still pretty high. My Acura is 10.5:1 and requires 91+ octane to keep it from knocking per mfg.
 
#52 ·
I've run 93 (or maybe it was 98) through a few tanks and it did seem like it was running better at times, but it could be placebo, I wish I could try having someone else fill my tank with either premium or regular and see if I can actually tell. Next time I fill up I'll try premium again and watch the timings. I also am taking it back to the dealership again today for round 2 and see if they don't just give me the same 'that's just how gears work" again
 
#54 ·
Good day guys, I have the same problem here with 2018 Impreza Manual transmission 16 800 KM on it. It's my girlfriend's car so I just noticed it today, she had told me a few times that it seemed to her that the car was not so powerful and asked me if it could be the A/C. She had described the symptom of it kind of jerking and having no power but I was telling her it was normal, blah blah, it's not a powerful car only 152HP... and then we went to Home Depot today I was driving and on the way back I experienced it, it felt like the clutch was slipping almost around 2500 RPM I floored it WOT with traction control OFF to see what is this abut and there is a long delay from about 2500 to 4000 RPM.

I would like to know now if this “upper engine/upper cylinder cleaner” is something that Subaru is aware of and willing to execute right away after me describing the symptoms or I will have to convince them ?

I have had 7 Subaru's , I presently have 3 in the driveway and it's the first time I see that. I must say that I am not impressed by this Impreza 2018. I have had Check Engine Light come on at 6000 KM for a **** Active Shutter Grill stuck and the same evening the Low Oil Level Message came on, we booked an appointment at Subaru Dealer they opened a oil consumption test but I am following myself the oil consumption and it did not consume any more oil after that. I did the next oil change myself at 14 000 KM because I had the impression that they had overfilled the oil to Maximum mark.

Thanks for all the information.
 
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