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Misfire in specific rev bands


Ric
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(2006 impreza R Sport, 2.0 N/A EJ204 with avcs)

Ive got a strange issue with the engine running rough, and misfiring a lot, juddery acceleration, but almost completely between 2500 and 3500 revs. No issues outside of that band.
Its had a new O2 sensor this year, which didnt cure the problem, and fuel system cleaner only helped for about a week or so.
It doesnt show up any error codes, and has stumped 2 mechanics so far, and cant seem to get a definite answer.
I dont want to keep throwing money at lots of parts for trial and error, so wondered if anyone has ideas?
Thought about disconnecting MAF to see if this helps, but some people said subarus often dont even run without it?
Likely causes im assuming would be either injectors or coils, but I dont want to spend out on one, to find it was the other.
FreeSSM shows no faults, BTSSM app shows lots of faults for stuff my car doesnt even have, so not sure whether to trust that app. That one shows slow response errors from almost every sensor on the car (plus ones I dont, DPF for example)
Not sure what the next step to take, dont want to have to pay main dealer prices if I can help it.

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Don't know much about n/a scoobs tbh but I'd say to check the spark plug condition and colour . As it can tell you quite a bit about how a engine is running and if 1 plug is a different colour it can help diagnose a particular cylinder at fault .

On turbo versions with avcs there's a "screen filter" in the avcs oil line banjo bolts. These are fairly prone to blocking and can starve the turbo or avcs solenoids of oil . Which in turn might cause rough running at certain rev ranges , it would normally would be accompanied by a code but might be worth a look  .

Check Engine earths , sensor plugs and engine loom plugs , as a dodgy connection might cause the multi codes btssm app too 

 

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Ok, thanks, plenty to be looking at. The strangest part of it is that it is far worse when running on premium fuels. If I put in standard fuel, it runs a lot better.

Sent from my CLT-L09 using Tapatalk

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Yeah, like minds think alike, they were changed when it first started happening, around the same time the fuel cleaner went through. Didn't notice any of the old ones looking any worse than the others at the time

Sent from my CLT-L09 using Tapatalk

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