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Rough idle !!!!!


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11 replies to this topic

#1 magnoman

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Posted 21 September 2004 - 09:00 PM

I have a 98 outback. about year ago it started to idle rough intermittent. the the rpm will drift slightly from 700 rpm and the whole car will start to shake so bad at lights I have to put it into N or park to get it to stop shaking! other wise the car runs great. its worse with Ac or defroster on. No engine lights are on. I have had it to three differenent dealers and they just stratch there heads! . the last one checked the motor mounts. I have had a full tune up. Injection service still shaking. agian its not all the time?
Please some help !!!!!!!!!!! It getting to the point of getting ride of the dog
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#2 sasquatch

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Posted 21 September 2004 - 09:21 PM

I have a 98 outback. about year ago it started to idle rough intermittent. the the rpm will drift slightly from 700 rpm and the whole car will start to shake so bad at lights I have to put it into N or park to get it to stop shaking! other wise the car runs great. its worse with Ac or defroster on. No engine lights are on. I have had it to three differenent dealers and they just stratch there heads! . the last one checked the motor mounts. I have had a full tune up. Injection service still shaking. agian its not all the time?
Please some help !!!!!!!!!!! It getting to the point of getting ride of the dog
Posted Image


first check the vacuum hoses to the pcv, to the throttle body and the IAC, make sure the PCV is okay (check for vacuum with car running), I've been advised on this site to spray brake cleaner into the lower hose connection. Also maybe use a volt tester and check power to the pins of the IAC

I'm betting vacuum issue.....

#3 coloradosubarules

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Posted 21 September 2004 - 09:45 PM

All else fails....crack up the idle set screw. I did.

#4 jcniest5

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Posted 21 September 2004 - 10:54 PM

It's probably the culprit of the IAC.

#5 magnoman

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Posted 22 September 2004 - 08:16 AM

I have checked all hoses and PCV. would the IAC give me a check engine lite?

Some one said may be 02 sensor. & that would not send a error code .

#6 SVX_commuter

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Posted 22 September 2004 - 11:47 AM

Well I was looking for threads about rough idle.

Your problem sounds similar to one I saw in another thread about rough idle in gear. Search on this "idle vibration--in gear only" and see if it helps you.
(I am not sure how to copy a thread title from a search page.)

#7 magnoman

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Posted 23 September 2004 - 08:17 AM

Thanks for the info. I checked out that thread. I just had both my front axels replaced not to long ago. so I do not think its that. When the idle goes down and runs rough it will start to make a low rumble sound & and you can hear it start to miss from the exhast pipe. I think it must be some kind of emission sensor. would a o2 sensor give me any think like this.

#8 ScoobySchmitty

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Posted 23 September 2004 - 08:25 AM

I've had IAC problems since day 1 in my MY91 Legacy, and it does control the idle (IAC: Idle Air Control). My problems have been that it will not idle properly cold, and will idle low and roughly (around 100-200 rpm) with the AC compressor engaged. Sometimes it won't idle at all with the compressor on, it will just quit on me! SPECULATION: I read a post earlier this week about the Outback having 2 O2 sensors. The 2nd one makes sure the 1st one is working right. If the 2nd one has stopped working first though, it leads me to believe that if the 1st one goes, then you have no way of knowing. PLEASE NOTE THIS IS SPECULATION, it might work differently for two 02 sensors. However, you cannot rule out the possibility that one of them might have gone bad. Hope this helps out.

#9 friendly_jacek

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Posted 23 September 2004 - 08:26 AM

I had the same problem in my old mazda. The idle speed adjustment were useless, since ECU would override them. The only thing that helped some was throttle body cleaning and thus, I strongly recommend doing that. I got rid of the car nevertheless because I was tired of it.

#10 shortlid

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Posted 27 December 2004 - 03:06 PM

What is the current consensus on using aerosol Throttle Body Cleaner on Soobs? I know I asked this question on ultimatesubaru.org like two years ago and the over whelming answer was NO!! That Subaru had some sort of special coating on the throat of the TB. And you would remove it if you used TB cleaner on it? My ’98 Legacy L wagon with EJ22, AT and 140k on the clock is idling rough now. I have replaced everything I can think of. New fuel filter, PCV valve, NGK plugs (gapped correctly), Brand new 640 CCA battery, in tank high end fuel injection cleaner, plug wires are in good shape. The only thing I can think of is a dirty TB. And now when it is cold it does that slightly surging thing, which the usually shake in gear at a stop sign??

#11 Chip

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Posted 28 December 2004 - 04:40 PM

My 98 O/B does the exact same thing. I'm thinking it's more transmission than motor. The fact that it idles smoothly in N leads me to believe it has something to do with the torque converter.

I switched to Mobil1 synthetic tranny oil and it helped a bit. It was also shifting into 2nd gear with a "thunk" but the new oil pretty well took care of that.

#12 Skip

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Posted 28 December 2004 - 05:13 PM

Have any of you thought to look at the EGR valve?

Do these have EGR valves?

The test for the EGR valve is to open it manually
with the engine warm and idling.

If the engine stumbles and tries to stall

it means the EGR valve is closing as it should.


Sounds like your EGR is not closing -
probably due to
crud build up on the pintle and seat.

It must be removed to clean it.

Some older Roo's have an EGR light to remind you to clean it.

Just a WAG




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