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Old 02-23-2012, 11:08 PM   #1
PhamilySedan
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Default 2002 Impreza 2.5RS Having Hesitation/Idle Issue

Hey fellow NASIOC'ers,

I've been trying to tackle this problem for a LONG time now. Since about November my car has been sitting because it's been giving me these two problems. The first problem was that I was leaking oil through my spark plug gaskets. I just re-did the valve cover gaskets and spark plug gaskets as well as brand new spark plugs today.

The real problem lies hear. On a cold or warm start, the car will idle just fine until a few seconds or a minute passes and then the idle gets REAL rough. Sounds as if it has a HUGE cam in it haha It won't die but it does a real steady hard idle. If you count "one" then "two" real slow, that's about how rough it idles. Also, this is probably related to the idle issue. When I accelerate the car bogs/bucks hard. For example, if i'm at lets say 3K RPM, and i'm trying to get it to 4K RPM, it'll start bucking/bogging anywhere inbetween until it reaches a higher RPM. (Not at any certain RPM but at any random RPM) I'm thinking that this might be a bad O2 Sensor?

I thought that the bad spark plug gaskets were causing the misfire, but nothing has changed after I replaced those today. Any help would be greatly appreciated because I miss driving her haha C'mon guys help me out!
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Old 02-24-2012, 06:28 AM   #2
Flat-4-Life
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i have been having the same problem for about the pas 2 months or so i finally broke down and took it to a shop and it seems that i have a bad ecu i am going to subaru this morning to verify it is the computer.
just so you know i have replaced my maf, iacv, both o2 sensors, all spark plugs, the ignition coil, spark plug wires, valve cover gasket, cleaned the throttle body and intake manifold and seafoamed my engine, replaced all vacuum hoses, the crank pos sensor and fuel filter.
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Old 02-24-2012, 10:12 AM   #3
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I'm having the same problem 99 legacy 2.5 Dohc.
I had a code for knock sensor and misfire. I replaced knock sensor and the misfire and rough idle ect persisted. Then I replaced the Maf sensor. No luck.


Now ive got a misfire code, the code scanner was also flashing egr Cat and 02 on the top of the Code reader. So im wondering where to go from here. I've heard someone say the egr was causing this on there car and they soaked it in brake cleaner and it fixed it so I'm gonna try that tonight.
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Old 02-24-2012, 11:37 AM   #4
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Sounds good guys.

Flat-4-Life, i'be also replaced the IACV, spark plugs, VC Gaskets, and what not. Sounds like we might have the same problem. Please post back if it really is your ECU! Next thing that i'm going to replace are the O2 sensors. . haha
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Old 02-25-2012, 09:17 AM   #5
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Bump!
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Old 02-25-2012, 01:44 PM   #6
Elbert Bass
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If the spark plug wire ends were soaked in oil by the leak and I have a misfire then I usually check plug wire resistances. #1 =5.6k to 10.6k ohms. #2 =7.3k to 13.7k ohms. #3 =5.9k to 11.1k ohms. #4 =7.3k to 13.7k ohms.

When you are measuring the wires look at the coil where the wires attach for burnt spots or white traces from the spark trying to jump. Bad wires can cause the spark to jump and physically burn the coil towers as well. If you need wires Subaru sells the whole set for a reasonable price. Replace the coil too if it is burnt and has been arcing.

If all that is OK then you need to start looking for vacuum leaks.
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Old 02-27-2012, 08:27 PM   #7
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Well I finally got a result back from Subaru they are saying that someone had rewired my o2 sensors to go opposite of where they should go anyway I replaced the rear one on my own and I could not do the front one myself so I took it to a shop and according to Subaru the shop i took it to could not do it either so they took out my new rear o2 sensor and put my new pre cat o2 sensor in then swiched the wires to cover it anyway try your o2 sensors and that should do the trick if it doesn't then I have no idea
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Old 02-27-2012, 08:34 PM   #8
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Tdagen have you done a compression test yet might help point you in a better direction also what cylinder/s are/is misfiring?? And if you are having vacuum leaks your car will not start at all and if it does then not for more then a second or two these engines need the extra compression that the intake manifold creates turbo or not
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Old 02-27-2012, 11:00 PM   #9
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That's what I'm thinking of trying. I've heard the first o2 sensor can drastically effect the way the car drives. Thanks for the input and hopefully that will solve my problem. I'll report back after I get the o2 sensor replaced
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Old 02-28-2012, 12:46 AM   #10
Flat-4-Life
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Good luck to you I should get my car back in the next couple days then again I am also getting my head gasket replaced lol
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Old 02-29-2012, 12:55 PM   #11
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could it be a tps out of adjustment? it would explain the rough acceleration but not the idle. hard to tell since flat 4 life replaced almost everything i would guess to check in the first place.
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Old 02-29-2012, 01:02 PM   #12
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also might want to try a power balance test on your injectors
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Old 02-29-2012, 01:56 PM   #13
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well i just got a call from subaru saying that it was the ecu like i had thought and now i am waiting on parts and i get a "brand New" car back. i hope this helps you in your search for the "truth" happy wrenching
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Old 03-02-2012, 05:05 PM   #14
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haha thanks Flat-4-Life. I have yet to do anything other than what i've stated before. Also, going to try and replace the upstream o2 and see if that works. If not, i'm going straight to the ECU haha THANKS!
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Old 03-02-2012, 07:10 PM   #15
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no prob i hope it works out for you good luck
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Old 10-26-2012, 10:29 PM   #16
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I know this is old but was the problem found and fixed?
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Old 11-07-2012, 09:24 AM   #17
Daniel_DeWitt
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I have this exact problem.

Replaced front o2 sensor, and idle air control valve. Don't know where to go from here :/
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Old 11-07-2012, 10:08 AM   #18
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i had the same problem with my 02 rs, replaced fuel filter, plugs, wires, coil, and front o2 sensor, cleaned the throttle body and replaced the idle air control and it was good as new. have done over 1k miles since and still no problems
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Old 11-07-2012, 11:26 AM   #19
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i take it everyone with this problem has either an intake or exhaust system on their car? i have a full header/exhaust and i'm thinking it's due to the increase air flow to the O2 sensor. my car does not like the cold wet seattle weather. when the weather dips my check engine light flashes during idle. it's been a little warmer in seattle as of late and my check engine light hasn't flashed in a week or so. weird stuff =T
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Old 11-07-2012, 12:32 PM   #20
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I do have an exhaust but it has been on for months before this problem occurred. Not sure if that means anything but yeah..
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Old 11-08-2012, 12:22 PM   #21
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my rs is completely stock and i got this problem, could always check fuel pressure to, make sure theres enough
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Old 11-09-2012, 07:44 PM   #22
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Fixed my problem today, THROTTLE POSITION SENSOR!
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Old 11-09-2012, 09:55 PM   #23
mikemace1976
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Angry My Stock '05 RS 2.5 idles At Almost 0.....

My completely stock 2.5 RS has been idling at almost 0 RPMs for 3 days now. Ever since it was towed and the tow yard left the dome light on killing the battery. They had to jump it when I picked it up and it's been like that ever since. The car never had any problems until this incident. Car has 85,000 miles/136794km on it and has been maintained well. I've had the battery disconnected plenty of times and I know all about letting the car relearn to idle, this isn't the case. Help me please!!!!
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Old 02-18-2015, 09:53 AM   #24
Zaraia
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Default my 02 RS and my discovieries.

Im sorry i know im kinda late to the party but After i decided to trade my audi a4 for my new baby (02 RS 2.5 awith 32k miles), it started having the same problems, it still has the same problems but im kinda curious as to what causes this because i had test driven the car several times before i actually bought it and it never gave me these problems, it only does it after the car has warmed up because when its just turned on it doesnt happen. A few days ago me and my dad decided to check the tps and the iacv, when we took out the iacv and cleaned it the car started idling at higher rpm's, before it idled at 500 rpm's and now it idle's at 1500 or so. Therefor i decided to buy a new iacv. If that doesnt work ill buy a tps and see if that fixes it.
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Old 10-21-2017, 08:38 AM   #25
Ivany97
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Default 2005 2.5rs idle/acceleration issue

Whenever my battery is disconnected from the car it canít properly relearn itís idle. Iíve let it run for 20 minutes and itíll idle around 350rpm and then as soon as you tap the gas it wonít recover properly itíll just die. Itís actually still drivable, itís just brutal trying to drive a standard car with no neutral in traffic. It also sort of skips and spudders down low, like if Iím rolling off the clutch or under any kind of load like bottom of second gear going up a slight hill ltíll chug for a second and then once I get up to a high enough rpm itís fine. I should also mention that there is a code for the upstream o2 sensor, I installed a new one last night and cleared the code and the problem still persists. Iíve also cleaned the maf and cleaned the throttle plate and still nothing. Iím taking an automotive course and my instructor believes itís something to do with the ecu but idk. Really frustrating so if anyoneís solved this issue please shed some light!! It sucks when you have to turn your car back on 30+ times in traffic just to get anywhere.
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