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99 Forrestor
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13 Posts
Discussion Starter #1
Wonderful forum you have here.
I'm a long time lurker on this site, but now need to get some answers.
My '99 automatic has developed a hesitation/stumbling problem, usually when cruising then getting back on the throttle around 2000 rpm under a bit of load, say going up a hill. Also does it when first pulling away after backing down the driveway it the morning. Doesn't do it when tranny shifts down say going up a hill.
My feeling says it is a O2 sensor- feels like a momentary over rich issue. Problem was getting progressively worse but didn't do it everytime under the same conditions.
Codes pulled read as follows PO325 - knock sensor
PO443 EVAP purge control solenoid
PO440 EVAP control system
Replaced knock sensor and problem still remains although it feels slightly better.
Tail pipe is a bit black.
Changed head gaskets and timing belt last year.
Any thoughts?
 

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The Modfather
2016 BRZ Limited - Manual 6 Speed Manual
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8,095 Posts
How many miles on the ODO? Could be the front O2 sensor. If you have say around 80K+ miles it would be a good idea to change it anyway. I find it helps with the MPG's regardless of having a code. Barring that have a look at the last or next to last post here:

http://www.subaruforester.org/vbulletin/f88/uh-oh-forester-sick-help-65277/index2.html

something you can easily check and either fix or rule out.

As for the other codes check your gas cap to be sure it's tight. And for he solenoid I have to think about that a little more
 

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Super Moderator
2007 Forester Sports XT 4EAT
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35,894 Posts
No CEL code P0420? :confused: I'd replace the front O2 sensor & I'd recommend a factory/OEM part. That sensor is critcal for correct engine operation, so I wouldn't try a universal replacement here. :wink:

Bobby...

My MODding Journal
 

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99 Forrestor
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13 Posts
Discussion Starter #4
Thanks for the quick responses. I'll change out the front 02 sensor and see what that does.
 

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99 Forrestor
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Discussion Starter #8 (Edited)
Well now things have changed. This morning when I started it cold it barely ran, seemed to be only on a couple of cylinders. Stalled when I put it in reverse and generally ran like crap. When it got above 3000 rpm or so it would run clean.
After the car was hot it will run close to normal with only the occasional hesitation/farting.
This sounds more ignition to me. But could it be the purge control solenoid?
Any thoughts?
 

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Super Moderator
2007 Forester Sports XT 4EAT
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35,894 Posts
Any CEL codes? When were the sparkplugs & wires last changed? Have you checked to see if anything was knocked loose during the O2 sensor replacement? :confused:

Bobby...

My MODding Journal
 

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99 Forrestor
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13 Posts
Discussion Starter #10
I haven't checked the codes again since I replaced the knock and O2 sensors so codes as the same as I stated in my first post.
It is quite difficult to start when cold and makes a very slight backfire through the intake manifold during the first few revolutions. Runs rough until it gets warmed up. Even after it's warm it will surge and hesititate from any sharp throttle input. It will surge under load as in going uphill or on level ground with the brakes on.
I'll change the ignition wires and plugs and see where that gets me.
It is a bit difficult, or getting more difficult to fill up the gas tank. Could this whole issue be the surge control solenoid as the codes suggest? If so I'll check for spider webs, fuel filler etc.

Thx for your input.
 

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Registered
99 Forrestor
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13 Posts
Discussion Starter #11
Ultimately turned out to be a broken #4 spark plug lead that had left a carbon track down the plug. Problem has been solved permanently.
 
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