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Car Forum / Ford / Ford Cars / July 2007

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5.8 high idle saga continued

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john - 24 Jul 2007 01:01 GMT
I made it through the weekend, and yes, it is still doing the 1500rpm
65 second runup during startup.  However, several times it started
normally.  The weather has been dryer here the past 3 days, so maybe
that is a factor, I don't know.

To Tom Adkins and Lugnut (if you'd care to answer):

1. Do you think it could be a bad EEC?
2.  Could it be a short somewhere?
3.  Is it possible it's linked somehow to humidity change, ie some
sensor sticking (TPS?).

I might throw another part at it.

Thank you,
John
aarcuda69062 - 24 Jul 2007 01:36 GMT
In article
<1185235317.720206.182920@n60g2000hse.googlegroups.com>,

> I made it through the weekend, and yes, it is still doing the 1500rpm
> 65 second runup during startup.  However, several times it started
[quoted text clipped - 12 lines]
> Thank you,
> John

Look at the power steering pressure line between the P/S pump and
the gear box, see if there is an electrical switch ported into
the pressure line.  If so, disconnect it and see if the symptoms
improve.
Tom Adkins - 24 Jul 2007 05:15 GMT
> I might throw another part at it.
>
> Thank you,
> John

 Offhand, If you're going to toss a part at it, I'd say TPS, Throttle Position
Sensor.  You're getting to a point where you will have to have it checked out, in
person, by someone qualified to do a diagnosis.
 The TPS is a "wear item" that can cause all kinds of strange symptoms as it fails.
It's ~$25 and will either solve your problem, or it won't. If it does not, it's time
to bend over and see your local dealer (or qualified Indy Shop).
john - 24 Jul 2007 23:09 GMT
> > I might throw another part at it.
>
[quoted text clipped - 7 lines]
> It's ~$25 and will either solve your problem, or it won't. If it does not, it's time
> to bend over and see your local dealer (or qualified Indy Shop).

Is the TPS just a bolt on - plug in part?  Do I have to "set" it, or
calibrate it?
lugnut - 24 Jul 2007 13:38 GMT
>I made it through the weekend, and yes, it is still doing the 1500rpm
>65 second runup during startup.  However, several times it started
[quoted text clipped - 12 lines]
>Thank you,
>John

I agree with Tom.  I think the only part I would just throw
at it at this point is the TPS.  Fairly cheap and easy to
change.  They can get flaky and fail w/o setting a code.  I
have seen them hold 30-35 mph after the throttle was
released and not set a code.  You may want to pin the wires
on it after you replace it to be sure the voltage at idle is
correct.  IIRC, it should be around 0.5 VDC.  Around 1.0vdc,
the ECM starts the off idle sequences to advance timing,
increase fuel and other chores.  The ECM's are pretty
reliable and not prone to failure.  More often than not,
ECM's that are replaced do not correct whatever the problem
might be.  IMHO, the Ford STAR tester is more capable than
any other tool on the market on Ford products.  A
knowledgeable teck should be able to find the problem with
it.  Most of the dealership in my part of the world will
apply the diagnostic fee toward the repair.  At this point,
I think it is probably worth your time and money to get this
done.  There are cases where a temporary breakout box has to
be installed to find the problem.

You may also want to follow up on 'cuda's suggestion because
the ECM does increase idle to compensate for steering
pressure.  A stuck switch can do this and the check is
quick.  This should also show up on a complete diagnostic.
john - 25 Jul 2007 18:05 GMT
> On Mon, 23 Jul 2007 17:01:57 -0700, john
>
[quoted text clipped - 39 lines]
> pressure.  A stuck switch can do this and the check is
> quick.  This should also show up on a complete diagnostic.
where exactly is the TPS on a 95 5.8?  This is a California truck, if
that makes a difference.
lugnut - 25 Jul 2007 21:13 GMT
>> >I made it through the weekend, and yes, it is still doing the 1500rpm
>> >65 second runup during startup.  However, several times it started
[quoted text clipped - 39 lines]
>where exactly is the TPS on a 95 5.8?  This is a California truck, if
>that makes a difference.

Should be on the bottom of the throttle body.  You will need
to dismount the throttle body from the intake to get at it.
The water hoses should have enough flex to avoid
disconnecting them.  You will probably have to disconnect
the EGR valve assembly.  The TPS is held on by a couple of
Phillips head screws.  They are usually pretty tight.  If
the TPS has never been replaced at 150K, it is probably due.
They do wear because they move just like an old radio tuner
every time the throttle is moved.  The TPS is simply an old
fashioned potentiometer that slides a contact over a coil of
wire to change resistance.

See my post on the manifold.  If you do one of these, yopu
may as well do both. Gaskets, TPS and supplies are probably
less than $50 to do both at the same time and you will be
finagling several of the same parts to do either repair.

BTW, while you are working in that area, you will see an
idle adjust screw on the top of the throttle body.  Unless
you know exactly what and how you are doing whatever, resist
all temptation to touch it or change it.  It is set using
some very specific parameters and will have no effect on
your problem.

Good luck

Lugnut
 
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