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EJ251 loss power, stall fault catalyst/O2 / Air flow/mass / IACV ?

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so things continue as this or similar from when i bought car.its about for 2 yrs now. i changed spark plugs, wires, petrol filter , LPG filter , air , oil changing as supose too and diff oils too. but from beggining i have some kind of power loss or lagging when wanna accelerate from stop. sometimes it goes fast and sometimes it thinks 1,2,3 seconds just then moves. 

i was reading what could cause that and such , was cleaning all intake parts and valves that can be cleaned there. 

i am getting just P0420 code what says bank1 error. so it kinda O2 sensor , but does front sensor can cause power loss , stall sometimes from no reason and lag in acceleration ? its sounds more like air flow mass sesnor , or IACV . and then could that be bad catalyst. but again would catalyst cause all those symptoms ?

so i cleand IACV maybe 3 month ago. it was not so bad , but i cleaned it anyways and other valves and sensors too that people say in net could cause suchs problems. but just today my call stall in middle road. but then i stopped fast , put on P start engine again and it went as if nothing happens. i had stall engine before too before cleaning that IACV. 

so whats about that air flow mass sensor then ? i found as forester ppl talked about that this one can sause power loss and lagging with moving car. 

and error says its kinda front O2 problem. but thats kinda not very much as O2 does . 

or could it be both sensor like air flow and IACV ? 

whats else then . 

and more important is there any simple ways to test those parts for fault ? i heard to test catalyst you remove front O2 sensor and try drive as that. if power comes back then its catalyst fault. can it be true this test?

when i wanna car go quick and floor to metal car sometimes doesnt even move for like couple seconds. then when i want to overtake other cars i need to really floor it pedal full. and then it does something ... i thought it might just gearbox kinda slugish but then i read all those people have similar problems too. 

thx all . 

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Can you run with exhaust disconnected? That will test the converters.

Yes, a bad MAF may cause car to stall and then restart and run fine.  But in USA, EJ251  are MAP-based engine control;  Not MAF.

O2 sensor may cause some problems too, but usually only when car is at operating temperature (warmed-up), I've read.


Read this Post: http://www.subaruoutback.org/forums/66-problems-maintenance/49537-p0420-diagnosis.html



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but what about bad accelerations like slow one . tested other day and my times are kinda bad 0-30mph in 10s. and 0-60mph in 17-19s. i mean even some 1997 legacy does 0-60mph in 10s. ir even less. i know old car losing power and such but thats some problem out there. even if its not stall. because now its not stalling but you can feel you lack power. you need press pedal to metal for car to accelerate. compare to this some mazda 323f with 1.5 engine goes like rocket.

people saying its O2 sensors. but does that all problem here. car goes same cold or hot no matter. sometimes it goes ok from stop but then after time looses that power. bad power when need to overtake too. like from 80 to 100km/h really problems 

Edited by scalman

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That's why I asked about disconnecting exhaust...that removes any CC restrictions.


I know nothing about LPG-fueled cars...so hopefully someone else adds info.


P.s. POST this over in the main forum for more responses: http://www.ultimatesubaru.org/forum/forum/44-1990-to-present-legacy-impreza-outback-forester-baja-wrxwrxsti-svx/

Edited by wtdash

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disconnect exhaust on which part ? after catalyst or before it . it would be loud and no possible drive like that on street so how i could test it then.

i read somewhere that removing front 02 sensor and driving makes exhaust more free and it could tell you about catalyst. so maybe just removing O2 sensor and driving would be enough

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