2012 Subaru Legacy with a 2 litre NA lump(EJ204?) with a 6 speed manual that has poor performance between 2000-3000rpm, it hesitates then when you get to 3000rpm it accelerates as it should.

It has had new plugs and disconnecting the battery for an hour or so sees it return to proper running but it soon starts to stutter again.

Any ideas?

Cheers,
Lewis

 

it could be a small air/exhaust leak or a bad o2 sensor, after an ECU reset the corrections go back to zero then after some driving it learns the incorrect AFR correction leading to the poor running and stutter as it leans out before going open loop.

Anyone local have diagnostic kit you can plug in to check the a/f corrections and note the o2 sensor readings before/after reset?

 

Interesting thanks, there are some good garages nearby that I will speak to.

 

Subaru dealer updated the software and the car now drives perfectly, a cheap and easy fix in the end.