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Lurching/jerking continues - what to try next?


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15 replies to this topic

#1 wondercow2

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Posted 08 January 2007 - 07:11 PM

In the two years I've owned my car (98 Legacy L, 2.2l/5MT), it's been making a sort of jerking when I let off the gas and then give it a little more, or when I'm trying to maintain a constant speed at very light throttle. It's REALLY annoying, and I think it's considerably more pronounced than "normal" manual transmission jerking. Other than this, the car is problem free- smooth runnning engine, perfectly shifting transmission, synchros work alright, axles seem to be in good shape. I've gotten sound advice from a lot of folks (including here) that it's from slop somewhere in the driveline, so I've been hunting down possible problems.

So far, I've replaced the clutch, inspected the wheel suspension (struts/shocks and related bushings), replaced the motor mounts and tranny mount with WRX bits (dogbone looked fine, and had no signs of wear or excess play in the bushings). I did not replace the transmission-to-crossmember mounts, as they looked great even after 130k.

What's next? I'm thinking about the rear diff mounts, except that the kind of "clunk" that the WRX crew seems to talk about is related to shifting, not throttle. Could the problem be at one of the joints in the driveshaft? Or is it (as one guy told me) just a fact of life caused by finicky computer engine management that doesn't like that grey area between light throttle and engine braking?

#2 tcspeer

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Posted 08 January 2007 - 07:27 PM

Have you changed the plug wires?

In the two years I've owned my car (98 Legacy L, 2.2l/5MT), it's been making a sort of jerking when I let off the gas and then give it a little more, or when I'm trying to maintain a constant speed at very light throttle. It's REALLY annoying, and I think it's considerably more pronounced than "normal" manual transmission jerking. Other than this, the car is problem free- smooth runnning engine, perfectly shifting transmission, synchros work alright, axles seem to be in good shape. I've gotten sound advice from a lot of folks (including here) that it's from slop somewhere in the driveline, so I've been hunting down possible problems.

So far, I've replaced the clutch, inspected the wheel suspension (struts/shocks and related bushings), replaced the motor mounts and tranny mount with WRX bits (dogbone looked fine, and had no signs of wear or excess play in the bushings). I did not replace the transmission-to-crossmember mounts, as they looked great even after 130k.

What's next? I'm thinking about the rear diff mounts, except that the kind of "clunk" that the WRX crew seems to talk about is related to shifting, not throttle. Could the problem be at one of the joints in the driveshaft? Or is it (as one guy told me) just a fact of life caused by finicky computer engine management that doesn't like that grey area between light throttle and engine braking?



#3 wondercow2

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Posted 08 January 2007 - 07:44 PM

Have you changed the plug wires?


Not recently- they're maybe 3 years old? I have changed plugs less than 10k ago, also replaced PCV and seafoamed the engine. Could plugs really be having a problem that only shows up in one particular driving condition??

#4 nipper

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Posted 08 January 2007 - 10:19 PM

I'm not sure what your issue is. When was the last time the fuel filter was changed. Also look at the driveshaft universal joint and carrier bearing.

nipper

#5 wondercow2

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Posted 08 January 2007 - 10:35 PM

I'm not sure what your issue is. When was the last time the fuel filter was changed. Also look at the driveshaft universal joint and carrier bearing.

nipper


Fuel filter was changed about 4 months ago, so I doubt it's a problem. I'll probably do the wires next time I change the plugs. But to clarify on the problem: when I'm trying to maintain a constant speed, usually at very light throttle, the car will lurch very noticably, as if it were an automatic that was awkwardly shifting. It's a big problem on the highway when I'm going down hill, trying to stay at the speed limit (with or without cruise control), although the jerking is less violent at highway speeds. The car is perfectly happy when it's accellerating or braking, or even engine braking over a long distance. If I'm actually trying to slow down, it feels fine when I slow down or downshift to match the speed. It's just that sweet spot when I give it a tiny bit more throttle to maintain speed that makes the lurch.

It feels as if I'm coasting in neutral and then suddenly dropping the clutch, except that the clutch is clearly out the entire time. Engine RPMs don't change at all, so I really don't think the clutch is misadjusted or anything is slipping. I'd be pretty disappointed if this was an engine-side issue (maybe something MAF-related?, because it feels like it's a mount or bushing problem. The carrier bearing sounds interesting- can it be checked without removing it? Do you just tug on the universal joint and look for play to see if it's defective?
Thanks for the help so far.

#6 keltik

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Posted 08 January 2007 - 11:09 PM

Identical problem here, in my case knocking the air con off helps a bit, the higher idle speed the air con demands makes it more noticeable in my car as im coasting down the main street in our town.

Looking over my car the only things i can put it down to are shot engine mounts. I dont really notice it in any of our other cars....

Either way i'll keep an eye on this thread in case any good solutions come up i can try. Its almost like the engine wont coast in gear at low speeds, it either wants to be accelerating or slowing down.

#7 Manarius

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Posted 09 January 2007 - 10:11 AM

Is it an engine lurch? Ie, when you put the gas on slightly, does the engine bump up significantly in RPM?

Would you describe it as more of a clunk (like a crappy shifting Auto) or more of a bang (like the engine shaking)?


#8 uniberp

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Posted 09 January 2007 - 10:27 AM

I'm wondering if it's one of the differentials binding (or both, alternately). How you'd go about checking that I have no idea other than removal and checking for any lash.


Fuel filter was changed about 4 months ago, so I doubt it's a problem. I'll probably do the wires next time I change the plugs. But to clarify on the problem: when I'm trying to maintain a constant speed, usually at very light throttle, the car will lurch very noticably, as if it were an automatic that was awkwardly shifting. It's a big problem on the highway when I'm going down hill, trying to stay at the speed limit (with or without cruise control), although the jerking is less violent at highway speeds. The car is perfectly happy when it's accellerating or braking, or even engine braking over a long distance. If I'm actually trying to slow down, it feels fine when I slow down or downshift to match the speed. It's just that sweet spot when I give it a tiny bit more throttle to maintain speed that makes the lurch.

It feels as if I'm coasting in neutral and then suddenly dropping the clutch, except that the clutch is clearly out the entire time. Engine RPMs don't change at all, so I really don't think the clutch is misadjusted or anything is slipping. I'd be pretty disappointed if this was an engine-side issue (maybe something MAF-related?, because it feels like it's a mount or bushing problem. The carrier bearing sounds interesting- can it be checked without removing it? Do you just tug on the universal joint and look for play to see if it's defective?
Thanks for the help so far.



#9 nipper

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Posted 09 January 2007 - 10:46 AM

IF its torque bind and its a manual, the only way to check it is by making a low speed full lock turn, just off idle. If you have to give it gas to keep it going or it bucks and jerks at idle speed you have TB. Other wise i would check the tranny mount, and the universals and carrier bearing in the driveshaft. Since you have a manual, you can remove the driveshaft and see if it goes away also.


nipper

#10 frag

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Posted 09 January 2007 - 10:58 AM

I remember this being discussed a couple of years ago on this board. Several members here were experiencing the same condition, me included and, IIRC, Commuter.
We came to the conclusion that AWD meant a lot of moving components between engine and wheels (trans, diffs, shafts, etc.) and that this was, for Subarus at least, the result of normal play in the system. Of course it does'nt get tighter as the car grows older. If this only happens when, at slow speed, you go from no throttle to light throttle and back, my opinion would be that this is «normal» in the sense that nothing you will do to your car - as seems to be the case up to now - will cure it.
My 2...

#11 frag

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Posted 09 January 2007 - 11:00 AM

I remember this being discussed a couple of years ago on this board. Several members here were experiencing the same condition, me included and, IIRC, Commuter.
We came to the conclusion that AWD meant a lot of moving components between engine and wheels (trans, diffs, shafts, viscous coupling, etc.) and that this was, for Subarus at least, the result of normal play in the system. Of course it does'nt get tighter as the car grows older. If this only happens when, at slow speed, you go from no throttle to light throttle and back, my opinion would be that this is «normal» in the sense that nothing you will do to your car - as seems to be the case up to now - will cure it.
For my part I learned to live with it by adapting the way i play with the gas pedal at slow speed.
My 2...

#12 unibrook

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Posted 06 February 2007 - 11:25 AM

I agree, I think this is the normal quirk of the car's transmission design. My 2001 Forester 5spd MT is the herky-jerkiest car I have owned. I still like it, willing to deal with it.

#13 Digger19

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Posted 13 February 2007 - 12:55 AM

My 97 Outback has been doing it for the better part of 5 years. Sometimes goes for weeks without a problem, then will happen daily for a few days then quit again. Especially noticeable after a glide down a long hill. Started 100,000 K ago and hasn't gotten any worse or better, so I'll live with it.

#14 unibrook

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Posted 04 June 2007 - 10:13 AM

My fix turned out to be the front 02 sensor. Here is my review from a diff thread: I have a 2001 Forester L with 85k miles on it. I have been chasing an intermittent hesitation under load problem for the past year since 80k miles. Only occurred when engine was warm. The front 02 sensor had been replaced once at 40k miles. I suspected it again this time, but since the only codes thrown had been cyl's 2&4 misfire ( p0302 & p0304) I assumed it must be ignition related. So I replaced plugs and wires 8 months ago...no effect. Did the dollar bill test over exhaust pipe, it was fine. Misted the coil, no sparks. I mentally sort of ruled out the fuel filter since it only happened when the engine was warm. Finally, a week ago while cruising on hwy at 65 mph, I felt the hesitation again (I wasn't even accelerating this time) and a new code was thrown....p0172. AutoZone read it for me, I described the symptoms to the guy and asked if he thought it might be the front 02 sensor. He said, "absolutely." So I decided to replace it next. Cost me $100.75 incl tax for the oem part# 22791aa00a from Cityside Subaru. I asked the Parts guy there if his experience was that this model engine needed a new front 02 sensor every 40k miles. He said, "no, these sensors are good for 100k miles." Well, bullsnot on that. I replaced the new front 02 sensor in 1 hour reaching from the top over the passenger side of the engine using an adjustable wrench. Be sure to use the thread lube so you can get it out easily next time.....after another 40k miles. I took out the air channel assembly first for better access. That seems to be the fix. No further hesitation since. Car runs like new.

#15 christopher G

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Posted 02 March 2008 - 01:01 PM

ok... so here is what I have done. I was woking on my buddies 98 forester MT, with a newer crate motor from japan, and it was having the exact problems that you were explaining. (and by the way.. you explained it well for such a undescribable "jerking")

the haynes manual pointed my to testing the TPS. although it only told me how to test a 4prong not a 3. but I know that most TPS's use about .5v at idle and 4.6-4.9v at WOT. so all I did was loosen the TPS and adjust it to the point I thought was right and it fixed the problem. well.. actually I adjusted it the wrong way at first and stopped while going down the road and re-adjusted it and BAM!!! No issues.. and the shifting all together was improved without the "JERK".

so, I hope that this may help people and point them in the right direction. although all the other things should be checked first.. ie, fuel filter, fuel pressure, quality of spark, motor & tranny mounts,etc.... but this was my fix..

ROCK OUT!!!!!!!!!!!!!:headbang:

#16 judamcadoo

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Posted 27 June 2008 - 02:00 PM

posted elsewhere, but might help:

Hello!

We had the "Elvis" hesitation when going up or coming down slight hills - "uh huh, uh huh, uh" as car was trying to shift to different gear or plain hestiatating

Subaru check transmission and all the other things to the wheels. Nothing. The sensors seemed OK, but husnband convinced it was a bad sensor someplace.

Then he noticed the tube from the air thing feeding the motor that was connected to the "pcv" was not a continuous rubber tube. it was splced, with no clamps on either end, and it was really loose. Probably leaky.

He put hose clamps on each end and VOILA! Smooth as the day we bought it.

He got the idea from his old truck, which had a bad "pcv" thing.

J. sends




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