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Old 12-22-2008, 05:40 PM   #1
kyle_g
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Default rough idle is giving me a headache - update 1/15/09: P0304 code shows up

P0304 code recently showed up - please read post #5

My 2000 Legacy (sohc ej25) has a very rough idle that refuses to go away, and I'm hoping someone can shed some insight on what could be causing it.

Here are the details:

- Once I give it gas and go, it runs like a champ.
- I've replaced the plugs, wires, fuel filter, air filter, and pcv valve.
- I've cleaned the throttle body along with the IAC valve. Neither made it go away, but cleaning the IACV seemed to help a little.
- I ran a compression test and all four cylinders came back the same (~160psi)
- I ran a full diagnostics test with a scanner and everything showed up healthy.
- All vacuum hoses, fuel lines, etc. are connected and where they should be.

I also want to add that when I give it gas, I hear what sounds like a few quick 'clicks' before actually revving up. It also does this when I start up in the morning, but the duration of the 'clicks' seems to be affected by how cold it was that night.

I have a video of it posted here: http://s445.photobucket.com/albums/q...ubaru033-1.flv

Along with the exhaust sputtering here: http://s445.photobucket.com/albums/q...ubaru034-1.flv

I'm all out of ideas, and it's really starting to give me a headache. I'm pulling the motor out next week to do my clutch, so I'm hoping I can figure this out before then. This way, I can replace or fix it a lot easier while it's out.

The only things left that I'm considering would be something that has to do with fuel injection, or something like a valve that's on it's way out.

Please help me out, I'll listen to any suggestions or ideas.

Thanks,
Kyle
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Last edited by kyle_g; 01-16-2009 at 12:07 AM.
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Old 12-22-2008, 09:06 PM   #2
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Test the TPS for a rough spot, likely around the idle position.

Jay
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Old 12-23-2008, 02:57 AM   #3
kyle_g
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Cool, I'll try that tomorrow and see if it does anything.

Thanks.
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Old 12-23-2008, 01:35 PM   #4
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I've got a couple TPS sensors, if you find you need one.

Jay
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Old 01-15-2009, 07:45 PM   #5
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Rather than starting a new thread, I'm just doing to add to this one.

Yesterday I had a CEL pop up - P0304 (cylinder 4 misfire). It came on right when I left for a 4 hour round trip, and the car drives the same as it did without the light.

The rough idle is still there, noticeable as all hell, and the exhaust sputtering is still there. However, like I said, it drives great.

I replaced the TPS as Storm said but saw no difference. I checked the plugs for proper gapping and replaced the wires again as they were "said" to be replaced by the previous owner. Still, no difference.

I'm stumped...this car only has 80k miles on it and has had all of it's required maintenance.

Any ideas...?
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Old 01-15-2009, 07:53 PM   #6
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What do the spark plugs look like when you pull them out? Are they carbon fouled? Just throwing this out there, but it could possibly be a front O2 sensor. If the sensor is bad, your car will run rich and make your spark plugs so carbon fouled that you will have misfires and a very rough idle. If the plugs aren't carbon fouled, then you can pretty much toss this idea straight out the window.
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Old 01-15-2009, 11:11 PM   #7
kyle_g
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Quote:
Originally Posted by rhino6303 View Post
What do the spark plugs look like when you pull them out? Are they carbon fouled? Just throwing this out there, but it could possibly be a front O2 sensor. If the sensor is bad, your car will run rich and make your spark plugs so carbon fouled that you will have misfires and a very rough idle. If the plugs aren't carbon fouled, then you can pretty much toss this idea straight out the window.
Plugs are good, no carbon. I also checked them for proper gap spacing when I did the wires too.

I don't want to throw that idea out the window quite yet though. I'll have to get the scanner out again and see what it reads for the front o2.

Until then, I'm going to try switching the #4 injector with the #2 and see if the CEL changes to a P0302 instead. If that is the case, we have a culprit. If it isn't, I'll be able to cross another possibility off the list.

Feel free to throw out any other ideas you might have. Thanks to MLK, I have one extra day to figure this out over the weekend.
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Old 01-15-2009, 11:41 PM   #8
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the coil pack/ignition module might be going bad mine died out of nowhere around the 80k mile mark easy way to check and not for the faint of heart (litteraly) is to yank the wire off while its running if you dont get a shock its good if dont it points more to the oxy sensor or the injector or an almost clogged fuel filter after that i dunno what to tell ya
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Old 01-16-2009, 12:04 AM   #9
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from the video you posted it sounds like your valvetrain . whats wrong is hard to say after only listening to your video , but definatly sounds like something in one of your heads.


at first it sounded like it wasnt firing on all cylinders but then at the end of it after it came back down to idle you can hear your valve train wacking away.

could just be excessive valve lash and needs to be adjusted . could be a rod too , hard to tell like i said with out being there ,

you said you havent gotten any cels which if is the case you shouldnt be that worried.

its a matter of trouble shooting now ,

1. any cels? no check
2. anything i can visually see ? no check
3. figuring out where the noise is origionating from?
4. busting out your mechanics stethescope and searching for the root of your problem.

the cool thing about subarus is they have 2 heads so if you dont know what your listening to you can compare it to the other cylinders . and then working from there .

eliminate things until you find it .
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Old 01-16-2009, 12:12 AM   #10
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ohh wait!!!!!!!!! didnt see post 5.

misfire huh hmmmmm and only on that cylinder .

do you have spark in that cylinder? take the plug out and keep it in the boot. have someone crank the engine and watch to see if there is spark.

CAUTION I TAKE NO RESPONSABLITY FOR YOU DOING THAT ! BE CAREFUL> I AM NO ONE > I AM A HOMELESS CRAZY ON THE STREET

if there is spark , good!

misfire? hmm i did say it sounded like it wasnt firing correctly when i heard it.

could be your coil pack, but it also could be mechanical . hard to say without being there.

see if you have spark in that cylinder that would help alot.
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Old 01-16-2009, 06:21 PM   #11
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Diagnostics test results:

Engine Speed.............................675 - 725rpms
ECT............................................... .......183 F
Vehicle Speed........................................0mph
Ignition Timing......................6.0 - 10.0 degrees (was always fluctuating)

Engine Load...........................................3.5 %
MAP (P)...........................................9.6 in Hg
MAF (R).........................................2.95 gm/s
TPS............................................... ......0.0%

IAT............................................... ........93 F
Fuel Stat 1...............................................CL
Fuel Stat 2.........................................Unused
ST FT 1................................................0 .8%
LT FT 1...............................................13 .2%
O2S B1 S2.........................................0.675 V
FT O2S B1 S2.......................................0.0%

MIL Status............................................ .OFF

I've bolded the ones I thought looked a little suspicious. Please let me know if you see anything out of order as my knowledge about all this OBDII stuff is very limited.

FYI: I cleared the check engine light when I did this and it did not come back on. Rough idle and exhaust sputtering...still there.
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Old 01-16-2009, 06:29 PM   #12
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As for the rough idle, do you have a cold air and is your car an automatic? My buddy has an automatic with a cold air intake and the cone filter is to close to the maf sensor. the turbine effect happens too early causing an air overflow past the MAF sensor and it causes it to idle like ****.

Note: That is a quote from him. If this reasoning is incorrect let me know so i can let him know
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Old 01-16-2009, 06:35 PM   #13
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Quote:
Originally Posted by subarumafia700 View Post
As for the rough idle, do you have a cold air and is your car an automatic? My buddy has an automatic with a cold air intake and the cone filter is to close to the maf sensor. the turbine effect happens too early causing an air overflow past the MAF sensor and it causes it to idle like ****.

Note: That is a quote from him. If this reasoning is incorrect let me know so i can let him know
No mods at all to the engine and it's a 5-speed.

It's the Phase II ej25 so it has a MAP sensor rather than a MAF sensor.
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Old 01-16-2009, 07:06 PM   #14
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that iat looks really high.

it is - temos here right now though. what was the outside temp that your reading 95 iat?
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Old 01-16-2009, 07:10 PM   #15
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wait why is your tps 0?

i see you just were reading at idle , i dont think that should be 0 though maybe 5v or something ?

anyone can confirm that the tps should have a reading + 0 at idle?
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Old 01-16-2009, 07:10 PM   #16
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Quote:
Originally Posted by watchunglava View Post
that iat looks really high.

it is - temos here right now though. what was the outside temp that your reading 95 iat?
It was about 65 outside when I scanned it.
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Old 01-16-2009, 10:45 PM   #17
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not that hight then. its negative 2 right now here so i was concerned maybe your temp sensor wasnt working correctly and fueling was an issue but nope.

hmmm

next step is doing a compression test on the cylinders.

do you have access to a cylinder compression guage?


one more question. you are using the correct weight of oil yes?

if your compression is fine and the ignition system( plugs wire coil ) all check out i would then look at the ecu itself as possibly being faulty.
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Old 01-16-2009, 10:52 PM   #18
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you said your injectors were fine right? i think you said that. try running some injector cleaner in your gas first . just to rule out the fueling. amsoil pi is good eats for your motor .

i see you have an obd scanner.

can you check out air fuel ratio with that?

or does anyone else know what the afr is for the voltage #'s this guy posted for the o2 sensor.


it now sounds to me like something to do with your compression.

do you have a coolant leak? is your oil foamy?

correct weight oil?

if not an its not the ecu , its defintatly internal , like a broken piston ring or piston it self , your crank could be worn ?

how many miles are on your motor again?
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Old 01-16-2009, 11:00 PM   #19
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Compression test has been done already too. Came back ~160psi across all cylinders. This led me to conclude that it's likely an electrical problem rather than a mechanical problem.

I've stuck to 5W30 full synthetic since I got the car. Previous owner ran the same stuff so I figured I'd keep it consistent.

I have a coil pack on hold at the parts store down the road. I'm gonna give it a try tomorrow, but if it doesn't do anything I'll just return it.

I honestly wouldn't be surprised if it was a bad ecu. If I'm remembering correctly, the roughness has been there ever since one weekend when I reset the ecu. I can't quite recall what I had done it for, but I do remember the car stalling out randomly and falling to almost 100rpms every so often when idling. It fixed itself within a few hundred miles but never really ran the same since.
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Old 01-16-2009, 11:09 PM   #20
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Quote:
Originally Posted by watchunglava View Post
you said your injectors were fine right? i think you said that. try running some injector cleaner in your gas first . just to rule out the fueling. amsoil pi is good eats for your motor .

i see you have an obd scanner.

can you check out air fuel ratio with that?

or does anyone else know what the afr is for the voltage #'s this guy posted for the o2 sensor.


it now sounds to me like something to do with your compression.

do you have a coolant leak? is your oil foamy?

correct weight oil?

if not an its not the ecu , its defintatly internal , like a broken piston ring or piston it self , your crank could be worn ?

how many miles are on your motor again?
Yeah, the scanner is one of those bigger, full diagnostic ones that belongs to my old man. It's definitely not a cheap piece of equipment, I can tell you that for sure Lucky for me I can go pick it up from him whenever I need it.

I'm not sure how to check the a/f ratio though. I'll see what I can do.

The injectors are another possibility still. As I said in post #7, I'm going to try to switch the injectors of cylinder 2 and 4 and see if anything happens. I might also have them flow tested as well.

Only 80 thousand miles on the motor. Drives unbelievably well though, so I don't think it'd be something like the crank or a piston or a ring or something like that. It's just the idle that gets me.

Thanks for all your help and ideas so far, watchunglava. Much appreciated.
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Old 01-17-2009, 10:35 AM   #21
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I don't like the value shown for the front O2 sensor. It very well could be boogered.

The IAT could be that high if the car was recently driven. Residual heat under the hood and all.....

You should be able to unplug each injector at idle, one at a time and note changes. It should get worse on a good injector and no change on the bad one.

Good luck!

Jay
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Old 01-17-2009, 12:38 PM   #22
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Well, it has 80K, when was the fuel filter last changed? if you'll have it out of the car, check valve lash(doesn't have much to do w/rough idle, just good to check), clean your crank and cam sensors. Search around for correct idle spark advance.

from the manual for rough idle:

1) Idle air control solenoid valve
2) Intake manifold pressure sensor
3) Intake air temperature sensor
4) Intake air temperature and pressure sensor
5) Engine coolant temperature sensor (*2)
6) Ignition parts (*1)
7) Air intake system (*5)
8) Fuel injection parts (*4)
9) Throttle position sensor
10) Crankshaft position sensor (*3)
11) Camshaft position sensor (*3)
12) Oxygen sensor
13) Fuel pump and fuel pump relay

*1: Check ignition coil & ignitor assembly and spark plug.
*2: Indicate the symptom occurring only in cold temperatures.
*3: Ensure the secure installation.
*4: Check fuel injector, fuel pressure regulator and fuel filter.
*5: Inspect air leak in air intake system.
*6: Adjust accelerator cable.
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Old 01-17-2009, 06:40 PM   #23
Tim Sanderson
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I know these engines tick but it sounds off to me.
One thing you have not done yet is a vacuum test. Just get a big face vacuum guage and attach it to whatever nipple it fits on on the manifold(not the fpr though).

You said the comp. test was a solid 160 all cylinders. That's good. A leakdown test would be more comprehensive though. Can you do one of those without great cost?

You might check the timing belt and also adjust the valve lash.
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Old 03-04-2009, 09:39 PM   #24
kyle_g
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I'm following up on this problem just in case someone experiences this problem again. It has now been fixed and the car idles extremely smooth now.

1/16 - Cleared the CEL, light never came back, but the rough idle was still there.

2/26 - Problem was still there, so I decided to bite the bullet and take it into Shingle Springs Subaru to let one of the top Subaru technicians on the west coast take a look at it. He tried everything, and compared my car to a few others with the same engine. The only difference he could find was a pressure sensor on the throttle body, but he told me it was so slight that there was no way it could cause that much of an issue, let alone the cost would've been outrageous had it not fixed it. Got my car back and they didn't charge me a penny. I guess I was just going to have to life with it for a while.

3/3 - CEL comes back on as I'm sitting at the stoplight. Pissed because it had only been a week since I let Subaru take a look at it. Never cleared the code or scanned it; made an appointment at the dealer for the very next day.

3/4 - Drop the car off. It's the same P0304 code, cylinder #4 misfire. It wasn't the ignition, and it wasn't the timing, so the only thing left they could think of was the valve clearance. Guess what? That was it! They took a brief look at it and all 4 exhaust valves were tight, #4 having almost no clearance whatsoever. Quoted me a huge amount, thought about it, went ahead with it and called them back. They adjusted the valves and replaced a bunch of seals and gaskets while they were at it. Get a call a few hours later the car is done and the idle is smoother than ever and the car runs much better. I couldn't have been happier.

Brought it home, they were right. The car runs amazing now Of course, my wallet isn't happy at all since my Bilstein fund went down the drain, but at least the engine is good now.

Thanks everyone for the help!
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Old 03-05-2009, 12:09 AM   #25
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thank you for following up. Although I hate to hear when people have to pay too much for easy service, it's good to know that it's fixed.
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