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Discussion Starter · #1 ·
So I bought this Impreza back in June and did the first oil change at 5000 miles after a 400 mile road trip. It's had some hesitation issues from a stop in 1st since new but after the oil change it got much worse. Quite frequently now under 3k RPM it has absolutely no power. Hills I can climb in 5th at 50mph when it isn't acting up can barely be climbed in 4th with my foot mashed right to the floor. I read somewhere that the problem has to do with the knock sensor and the computer pulling the timing back and killing what little power the engine had to begin with.

Finally put my code reader that does live data on it this morning and found that the timing was consistently being pulled back to 5-10 degrees ATDC.... no wonder the thing is a dog. This was happening around 2k RPM with throttle position at 25%+ climbing a slight hill. It would perk up once the revs climbed and the timing got to around 5 degrees BTDC. When it wasn't acting up the timing was around 8 degrees BTDC under the same conditions.

Has anyone else had a similar experience? And does anyone have any idea what causes the computer to pull the timing back that far??

I looked at the data from my old Jetta and that would never drop below 8 degrees BTDC which makes a hell of a lot more sense than what's going on with this Subie.

I hesitate (hah) to bring it to the dealership since it's an intermittent problem and there is no check engine light but this needs to be fixed, I can see it being dangerous under the right conditions.

Thanks,
Ryan
 

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Discussion Starter · #3 ·
I imagine it could be emissions related but there is definitely something wrong here. I don't think anyone would classify what this car is doing as normal behavior. Especially from a new car.
 

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Brand new impreza here too, I notice it and find it to be normal. You're asking for power under load where the engine isn't able to produce it. In fact you can probably hear slight pinging before the stumbling, that's why the timing is backing off so much. I can hear detonation under these circumstances with the windows open and no music and replicate the stumbling. Doesn't bother me, just bring the revs up and ask for power when the engine can give it. I'm pretty much hovering 4 to 5 k on any decent acceleration and never had issues that way. I haven't tried 91 gas under low rpms and high load but I imagine there would be a difference in timing reductions.
 

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Discussion Starter · #5 ·
I haven't heard any ping with mine and believe me I've tried to listen for it. If the issue were just asking the engine for more power than it can deliver then why would it only be an intermittent problem? I've also tried 91 octane and it makes no difference in performance or timing. I think the issue lies in the factory tune. I'll be calling the dealer soon and see what they say. If they say it's normal then I'll be ditching this thing as soon as I can... which is a shame because I really like they way the engine is laid out for serviceability and it's just a nice car to drive when it isn't acting up.
 

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My only suggestion that you can try right away is keeping the rpms up above 3k before loading, give it a try, the higher the better. I think it'll perform better. Just this morning I had the stumbling because I forgot my own advice, 2k in 5th giving a bit of throttle and it's even more touchy if the ac is on, nearly instant. After having a quick look at the compression of the fb20 I'm not surprised at all, with a ratio of 10.5~ the engine is nearly always on the edge of knocking and easily aggravated with low turning speeds and low vacuum. Plus having a 5mt is contributing to it simply allowing these conditions to be met more easily. If you decide to try my advice I look forward to seeing the results.
 

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Had the exact same problem, confirmed timing being retarded with a Bluetooth scan tool. Only happens when engine is warmed up, seems to correlate with intake temp (which is why it seems worse after a hot restart when the whole engine bay gets heat soaked from sitting with hot engine and no airflow). ECU seems to learn which conditions have caused knock in the past and retard timing under similar conditions (hot intake air, low speed and high load...).

Here is how I fixed it last summer : when empty, fill up with 91 octane then run it a bit to purge fuel system of old fuel. Reset ECU by unplugging the battery and do idle relearn procedure (check on YouTube).

Haven’t had the problem since, switched back to 87 octane for the winter so I will probably have to redo the procedure one it starts getting hot again next spring.
 

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Just had the same issue. Did an oil change and an engine idle re-learn and the issue is gone.
Engine Idle Re-Learn process...
1. Un hook negative battery cable for 30 minutes
2. Re-hook battery
3. Turn of ALL loads (A/C, radio, interior lights, etc.)
4. Turn key to "ON" position for 15 seconds and let the throttle body go thru its checks.
5. Start the car and run for 10 minutes (with no loads)
6. Shut down car
7. Turn car back to "ON" position for another 15 seconds.
8. Start car and run for 5 minutes (with no loads).
9. The process is finished
10. Also started running 93 octane in the tank.
 

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Just had the same issue. Did an oil change and an engine idle re-learn and the issue is gone.
Engine Idle Re-Learn process...
1. Un hook negative battery cable for 30 minutes
2. Re-hook battery
3. Turn of ALL loads (A/C, radio, interior lights, etc.)
4. Turn key to "ON" position for 15 seconds and let the throttle body go thru its checks.
5. Start the car and run for 10 minutes (with no loads)
6. Shut down car
7. Turn car back to "ON" position for another 15 seconds.
8. Start car and run for 5 minutes (with no loads).
9. The process is finished
10. Also started running 93 octane in the tank.
There's a new TSB to address this. See Knock correction causing stuttering | 5th Gen Subaru Impreza Forum (impreza5.com)
 

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You beat me to it. :)
cbidwell91

Is there any OEM software update available to remove the "rev hang" that the manual transmission cars suffer from? There's aftermarket ability to remove this characteristic from the engine tune, but an OEM ECM tune update would be great for everyone.
 

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cbidwell91

Is there any OEM software update available to remove the "rev hang" that the manual transmission cars suffer from? There's aftermarket ability to remove this characteristic from the engine tune, but an OEM ECM tune update would be great for everyone.
Unfortunately we don't offer an OEM tune for that. Actually, we don't even make the tunes in house. These are all designed by Subaru Japan and uploaded into the ECU's by our supplier.
 

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Had these exact symptoms to the T :) I mentioned it to my dear service advisors …. However I get these looks— like I am looking at you - I hear you - but I am not really listening to you ;) Mine went away ( I think ) after a fuel injector cleaning and a tank of higher octane ….. but if it ever comes back I can’t wait to try this pathway …. thank you for these steps !!!
 

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Mentioned this to my service advisor , they didn’t even care about it or the number of the TSB …. It’s sad when people stop listening :(
Call/email subaru customer advocacy and let them know about your appointment and what you want fixed. Come in with the TSB printed out.
 
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