jerking and hesitation at low acceleration

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I have a 2000 OBW, 2.5L-5MT, approx. 180k km. Recently it's been
exhibiting some wierd jerking and hesitation behaviour. It seems to
occur mainly under slow acceleration or cruise control mode. If I'm
slowing down, a slow steady release of the throttle would at some point
produce a hesitating jerk. When accelerating, if I'm accelerating
slowly, it would also jerk. If I'm giving it some heavy gas, then there
would be no problem.

It also happens while in cruise mode. It seems that slight changes in
throttle position create disproportionately large acceleration or
deceleration. What could be the cause of this, throttle position sensor,
fuel, spark, etc.?

    Yousuf Khan

Re: jerking and hesitation at low acceleration



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Curious, did some numbnuts recently change your timing belt?  Tensioner?


I had these symptoms and over teh course of 9 months having gone
through changing plug wires, cam sensors, crank sensors, o2 sensors,
having the head rebuilt and the problem persisted.

Turned out to correlate back to a timing belt change with a new subaru
tensioner, and the belt jumping one tooth intermittently.

Getting any check engine lights/codes?  In my case the subtle annoying
crap yer talking about happened for a long long time before the car
would finally throw a code, usually misfire on a cylinder or 4, or
something pionting to crank or cam sensors.   All leading one on a
wild goose chase.

 
--
Todd H.
2001 Legacy Outback Wagon, 2.5L H-4
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Re: jerking and hesitation at low acceleration


On Jun 13, 1:25 am, snipped-for-privacy@toddh.net (Todd H.) wrote:
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No, I haven't had any numbnuts changing my timing belt yet. :-)

However, now that you mention timing belt, I remember I was told by
some techs at Mr. Lube, where I get my oil changed that they noticed
that the timing belt was getting frayed. I normally don't trust them
with anything other than oil changes, so I semi-ignored them.

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No, there's no check engine warning yet.

Re: jerking and hesitation at low acceleration


YKhan wrote:
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They couldn't find anything wrong with the drive belts, and the timing
belts were never exposed.

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Actually, I decided to take the car into the dealer finally, and the day
I took it in, the check engine light finally came on.

The dealer did some diagnostics and they are certain that the problem
originates with throttle position sensor on the throttle body. This one
is going to expensive, they are talking about $1300 for the part!

    Yousuf Khan

Re: jerking and hesitation at low acceleration


On Thu, 12 Jun 2008 23:33:01 -0400, Yousuf Khan wrote:

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sounds like a problem with the ignition system.  I would start by looking
at spark plug wires, then plugs themselves, then the ignition coils.  If
those are all good, then check the timing belt.

If all that is good, then start looking at the gas system like the fuel
pump/filter though its a bit soon for that.

Re: jerking and hesitation at low acceleration


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All of the sparkplug wires were changed a little over a year ago, when
I noticed a hesitancy early in the morning when first starting the car
up. Turned out that there were holes in the wire which were causing
short circuits when early morning moisture coated them. However, the
timing belt might be something to look into, as I was told during a
recent oil change that the belts were getting frayed.

   Yousuf Khan

Re: jerking and hesitation at low acceleration


On Sat, 14 Jun 2008 11:43:21 -0700, YKhan wrote:

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How well does it shift, or is this a manual?

I would look at fuel before timing to be honest.  especially since it is
not a continuous problem.  Does the car run any hotter?

Re: jerking and hesitation at low acceleration



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Also, what plugs were put in a year ago. If they were Bosch Platinums,
pull them out and throw them as far as you can. Put in the recommended
NGK or Nippondenso plugs. I have had that kind of trouble with just
about every set of Bosch platinums I've ever run across.


Re: jerking and hesitation at low acceleration


Hmmm, the Bosch plugs my father installed in his 71 Nissan Patrol, when
his car was relatively new, had the same problems.  German tradition
keeps up, ;)

clare at snyder dot ontario dot canada wrote:
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Re: jerking and hesitation at low acceleration


clare at snyder dot ontario dot canada wrote:
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No, I've stayed away from all of the gimmicky platinum spark plug stuff,
I have only replaced them with standard-issue NGK plugs so far. Besides,
the problem didn't occur after a spark plug change.

    Yousuf Khan

Re: jerking and hesitation at low acceleration


dnoyeB wrote:
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It is a manual, and it shifts horribly. That is one of the reasons I
noticed this problem. I'd often get a hesitation when starting off
slowly in 1st gear, but it would be fine if I floored it.

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The car isn't running any hotter, the temperature needle has remained at
its normal position throughout.

The dealer has told me the problem lies in a throttle position sensor
inside the throttle body. Seems to be a rare problem, as they had to
wait over a week to get the part in.

    Yousuf Khan

Re: jerking and hesitation at low acceleration


YKhan wrote:
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I would treat that information with a pinch of salt      The timing belt
is enclosed and there is no way of seeing "that the belts were getting
frayed" without removing the covers.  There is no need to remove those
covers when changing the oil.

Re: jerking and hesitation at low acceleration


On Sun, 15 Jun 2008 14:54:59 +1200, Bugalugs wrote:

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I assumed he meant the belts he could see were worn.  But true enough my
visible belts were work and I replaced them all.  Then I opened up my
timing belt cover and that belt was fine..


CL

Re: jerking and hesitation at low acceleration


Bugalugs wrote:
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Yeah, I found that out in a short enough time. When I took it back to
the place that said the belts looked frayed, they told me that the
timing belts are actually inside the engine and not exposed, so they
were probably only talking about the drive belts which run the
alternator and AC, etc. They also took another look at those belts and
said that this time they couldn't see any problem with those belts!
Well, that closed that avenue of investigation.

    Yousuf Khan

Re: jerking and hesitation at low acceleration


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I had similar problems with 94 Legacy and turned out to be a small
pinhole burned into one of the spark plug insulator boots. Good luck.

Re: jerking and hesitation at low acceleration


On Sat, 14 Jun 2008 11:10:46 -0700, Dan wrote:

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This is why I hang on to my old timing light.  You can put the light on
each wire as close to the plug as possible, and look at the flashes and
see if there are any misses.  Lets you know the cables are bad right away.

Of course it wouldn't catch a boot problem.

Re: jerking and hesitation at low acceleration


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Try disconnecting your front O2 sensor and taking it for a test drive. Power
will be down but if it's now smooth, replace the sensor. It's a common
failure item on these cars.


Re: jerking and hesitation at low acceleration


Dave wrote:
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The dealer seems to have traced the problem down to a throttle position
sensor on the throttle body. I hope they're right because this is going
to be expensive, they're talking about $1300 for a new throttle body!

I've been waiting over one week for them to ship the part into the
dealership. Interestingly, during that time, I've been driving the car
and the problem has been gradually going away all by itself. So I called
the dealer today, and asked if it's still necessary to get it replaced?
And he said he's absolutely certain that the part is going to fail
again. This dealer has been relatively reliable for me, so I'm inclined
to believe them, but crap, $1300 for a sensor problem?!?

    Yousuf Khan

Re: jerking and hesitation at low acceleration


On Wed, 25 Jun 2008 10:23:57 -0400, Yousuf Khan wrote:

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DAMN!!  You need a whole new throttle body just because of a bad throttle
position sensor?  That sounds crazy.  I never had to replace one though.  
Just sees high for a "sensor".

Re: jerking and hesitation at low acceleration


dnoyeB wrote:

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I would definitely investigate the neccesity of a TPS repair that
expensive. mayeb get a second opinion. If it IS required, try to get
your dealership to at least match an online dealer's price for the part
- check with jamie thru www.subarugenuineparts.com

Carl


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