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1998 forester s
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24 Posts
Discussion Starter #1
looking for someone who has cured their problem with a cold hesitation"feels like stuck in the mud" in first gear under light throttle at around the 1800rpm-2000rpm mark then kicks in and seems to clear up. seems to clear up once engine temp comes up, i've heard so many things to check i don't know what to do and would rather not replace parts i don't need, i did a tuneup, cleaned mass air, idle control valve and throttle body, seems like either engine is going lean or the timing is jumping around, these parts aren't cheap so if i can't figure something out soon i'm gonna have to take it somewhere that can run a diagnostic, please help, leaning towards a 02 sensor or faulty knock sensor but don't want to make a hundred dollar mistake, thanks in advance
 

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Super Moderator
2007 Forester Sports XT 4EAT
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35,958 Posts
I see you have 116K miles on your '98. Was the timing belt & associated parts chaned at 105K miles? Any CEL codes? :confused:

A front '02 sensor can be failing before it drops a code, but I'd expect it to be causing an overly rich condition & a P0420 CEL code from the rear 02 sensor. :smile:

Bobby...

My MODding Journal
 

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Registered
1998 forester s
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24 Posts
Discussion Starter #3 (Edited)
thanks for reply, i just bought the car with 114000 on it, are you thinking it might have jumped a tooth? don't have any history on the timing belt but it is on the to do list when the weather breaks since i understand this dohc motor is an interference engine and if the rubber band snaps it's a big money fix, no codes at present, right after i got it i had to really get into it to merge and it threw a code , something about cat under threshold, might have been 420, i cleared it and have been driving it for a month and light hasn't come back on, i have a scanner which gives live readings and it seems like the sensors fluctuate at idle, but i'm not really sure of what the correct values are anyway, i sold my 183k legacy to my brother and it too suffered from the same hesitation:icon_confused:
 

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Super Moderator
2007 Forester Sports XT 4EAT
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35,958 Posts
I'd be looking at the front O2 sensor, especially with symptoms you discribed. The P0420 code you had means the CAT was overwhelmed & the rear O2 sensor detects excess O2 in the exhaust flow. :wink:

If the timing belt wasn't changed at 105K miles, you on borrowed time! If it goes, you'll need a new engine! :icon_eek:

Bobby...

My MODding Journal
 

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1998 forester s
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24 Posts
Discussion Starter #5
thanks bobby, i was leaning this way, also fuel consumption seems a little high, about 16 city, and i don't drive very aggresive. guess at this mileage the front sensor has seen alot of use, got my tax refund so i'll give it a try if it ever stops snowing, we have been getting hammered in SE PA. when you do a t-belt, do you change everything? i was gonna do belt, tensioner and water pump, should the idlers be done or is that something more for a second belt change? thanks for the directional push i'll let you know if it helps the hiccup:rock:
 

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Super Moderator
2007 Forester Sports XT 4EAT
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35,958 Posts
Good luck on your DIY repairs! :cool:

I know what you mean about the weather. It's been very mild here this winter, even put the summer tires back on the Forester. Even had to start mowing the lawn & pruning the trees & shrubs. Now the weather decided to change back to rain when I was just getting use to sunny T-shirt weather! :frown:

Bobby...

My MODding Journal
 

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1998 forester s
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24 Posts
Discussion Starter #7
well i have good news and bad news folks, i got another 420 code, so i bought new o2 sensors and replaced the front o2 but the rear o2 plug didn't match up, i looked on the bosch site and the parts store computer was showing the correct part number. so i did some investigating and found that a downstream sensor from a legacy 2.5 has the same plug as mine , wierd, anywho, put in new front sensor and reinstalled old rear since it seem to work. still the hesitation, ughhhh, had previously went on just answer site and tech had mentioned that 1800rpm was about the rpm egr opens, so i unplugged and capped the vacuum to egr, drumroll.......... hesitation is now gone, bad news after driving a bit i got a egr flow code 400. what now? gonna repost with new info but if anyone sees this i'll be checking it, i have cleaned egr and it seems to work, the one thing i noticed is service manual says it should move around 1/8 inch and mine seems to pull more like a quarter inch, i see there is a vacuum modulator of some sort, looks like a flying saucer, with two vac lines going in, one out to vac control solenoid and a line running down to manifold near egr valve, anyway to test that or could the spring in egr be weak, or am i just plumb crazy?
 

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1998 forester s
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24 Posts
Discussion Starter #8
thought i'de update my findings. turns out that hesitation is still there even with egr unplugged, found a homemade connection on the knock sensor which looked corroded and was hangin on by a few strands, so i dumped another 90 $'s on a new knock sensor and configured a respectable connection, now i can't say for sure whether the knock sensor did it or the o2 sensor needed a coulple days to straighten things out, but it appears that the issue is now resolved. one down about six problems to go.haha thanks to everyone who responded,:woohoo:
 
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