Rough Idle

Posts specific to the 3.0 litre NA H6 engine

Rough Idle

Postby mattlib12 » Mon Nov 02, 2009 3:16 pm

Has anyone experienced their H6 idling very rough when they first start the car? This has only happened a couple of times to me and it disappears pretty quickly but just wanted to check that there isn't anything wrong. Both times it happened the car hadn't been driven for a while so I'm not sure if that had anything to do with it?
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Re: Rough Idle

Postby Ric » Mon Nov 02, 2009 8:47 pm

How long is "a while"?
If we're talking months, then the fuel can decompose (the "volatile" components evaporate off), but that would make it run badly until you put in some fresh fuel.
It would be useful if you could read out any diagnostic codes from the ECU. Do you know anyone with a code scanner or an ECUDatascan?

One possibility is a "sticky" injector, which is freeing up once the engine has been running for a bit.
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Re: Rough Idle

Postby mattlib12 » Tue Nov 03, 2009 4:52 pm

Not months, more like a couple of weeks. I thought it might be something to do with the injectors as well. Don't know anyone with a code scanner unfortunately.
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Re: Rough Idle

Postby specbtommy » Tue Nov 03, 2009 8:02 pm

subaru or a place that specializes in subaru will put there comp on it and test it and tell you whats wrong
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Re: Rough Idle

Postby todda189 » Sat Nov 14, 2009 9:46 am

Mine idles rough whern you first start it to !!
but i think ive heard somewhere that its to do with the rev limiter kicking in early whilst the car is cold so that u dont get in it and flog the living hell out of it !!
i find that if i put it back in neutral it goes away ?
My05 3.0RB , King springs , 20" Evulve c2 wheels !!
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Re: Rough Idle

Postby deucer » Sun Nov 15, 2009 1:18 am

Hey Matt,
Yes I had that problem once. Like you it was after not using the car for a couple of weeks. The idle had a bit of a niggle in it for about 6 seconds right after a cold start in the morning. Went away after a tank of regular use on 98 RON fuel and a bottle of Nulon Fuel System cleaner. Can't say what the cause was as it never came back.

Make sure your mechanic or Subaru are running the upper engine cleaner through the engine at every service. This is pretty important for Subaru's horizontally opposed engines as they have a tendency to collect gunk in the intake system/ valves.

Cheers,
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Ex MY05 3.0R-B Wagon... But Still in the Blood.
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Re: Rough Idle

Postby bennygsr » Tue Feb 09, 2010 10:46 am

Just had this happened today, for the second time (first time a few months ago).

Haven't driven the car over about 4 days, yesterday started it and moved it in the garage and turned it off again, and then the rough idle this morning.

It felt the car was being shaken apart. All good though after about 15 seconds.
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