1998 Subaru Forester light throttle hesitation at around 20

Tiny
THISOLDTRUCK2
  • MEMBER
  • 1998 SUBARU FORESTER
  • 4 CYL
  • AWD
  • AUTOMATIC
  • 116,000 MILES
Hello my new to me forester much like my previous legacy of the same year but had 180k, has a wierd hesitation on light acceleration around 1800-2200 rpm, feels like it's stuck in the mud, seems much more noticable when engine is cold, but ocassionaly feel it very slightly with a warm engine. I just bought the car and have new plugs and wires yet to put on but feels like either engine goes lean or possibly timing is backing off. I have read that it is possible the knock sensor could be picking up on the piston slap and backing off timing. Do you think this might be the case, my scan tool says 15 deg. Advance at idle, gonna see if it will record as I drive.I was thinking of unbolting knock sensor and tieing it off somewhere to see if it helps, also read about putting a rubber washer between sensor and block? I don't want to unplug it because i'm unsure if it would cause timing to be backed off all the time, does the knock sensor even work in a cold "closed loop" situation, or do you think I should be looking elsewhere, all vaccum lines are looking good egr is working fine, vacuum reads 20 at idle but flutters a bit, i'm hoping tune up will cure this, I replaced pcv, cleaned maf, throttle body and aic valve, tps reads around.5 at idle and 4.5 at full throttle, no codes, other than this runs pretty good, does shake pretty good at 800rpm in gear, enough to rattle door panels, but seems to smooth out as engine warms and idle drops down to around 650-700. Please help this thing is driving me nuts
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Thursday, February 18th, 2010 AT 11:09 PM

4 Replies

Tiny
JACK42
  • MEMBER
Definitly tune it up. The knock sensor cando what you describe, if the Subaru guys fix is the rubber washer I would give it ago, I have heard alot of knock sensor issues, just havent had to deal with any personally. When the engine goes lean from EGR around the rpm you described, it can make the engine ping a little. As far as roughness goes, check your motor mounts to be sure they are good. Is it only rough in the morning when first cold started? Does it use any coolant? Those have some head gasket problems too.
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Sunday, February 21st, 2010 AT 7:40 AM
Tiny
THISOLDTRUCK2
  • MEMBER
No it doesn't seem to have any head gasket issues, i'm gonna do a compression test when I do the plugs, I had thought about the egr, but it's vacuum line goes through a electronic module and from what i've seen doesn't seem to open utill engine is warm. I will disconnect and plug the line to see if there is an improvement, I plan on checking motor mounts when I due tune, just frustrated because with the weather we're having, I can't work on it properly, I think I just got a bad one, i've driven dozens of these car at my auto auction job and they almost all seem to run well.
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Sunday, February 21st, 2010 AT 2:23 PM
Tiny
THISOLDTRUCK2
  • MEMBER
I forgot to mention that the car vibrates less when warm becuse the idle drops down, even when warm if I hold my foot on gas and brake in gear and bring it up to around 8-900 rpm the vibration is still there
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Sunday, February 21st, 2010 AT 2:27 PM
Tiny
JACK42
  • MEMBER
If it isnt a misfire, then it may be bad mounts or an engine/trans vibration.
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Sunday, February 21st, 2010 AT 3:46 PM

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