Fast idle on Disco V8

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GWGY - 23 Dec 2007 06:21 GMT

My 95 3.9 automatice Disco has developed a problem with engine idle.

When the car is started the rpm will shoot straight up to about 2500.
It will then fall back to idle in about 500 rpm steps over a period of
about 10 seconds. This happens both cold and hot.

The same thing occurs when it is taken out of gear, Revs increase and
then drop in steps to idle. Of course when driving the same thing
happens when you lift your foot off the throttle. Vehicle just keeps
going for a few seconds befrore slowing. In fact you can feel it
pulling against the brakes (if you see what I mean!!).

With the vehicle stopped and engine idling normally, revving does not
show the same symptoms - revs drop straight to idle. Put it in gear
and the problem manifests itself, i.e. shows up under a load
situation.

Idle is not rough and doesn't hunt

Anyone any experience of this fault?

Cheers
Geoff

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Rich B - 23 Dec 2007 11:09 GMT

GWGY typed:

> My 95 3.9 automatice Disco has developed a problem with engine idle.
>
[quoted text clipped - 19 lines]
> Cheers
> Geoff

Stepper motor?

Signature

Rich B
Ducati GT1000
Take out the obvious to email me.

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GWGY - 23 Dec 2007 17:06 GMT

Have disconnected the stepper motor connector and the engine revs as
would be expected. It had occurred to me that the stepper motor might
be adjusting slower than it should, but I don't know if that is even
possible.

Cheers
Geoff

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max - 24 Dec 2007 07:10 GMT

I think you need to do more than disconnect the stepper, if it is stuck
open .... you need to close the air feed to it as well ???

Max

> Have disconnected the stepper motor connector and the engine revs as
> would be expected. It had occurred to me that the stepper motor might
[quoted text clipped - 3 lines]
> Cheers
> Geoff

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Rich B - 24 Dec 2007 09:50 GMT

GWGY typed:

> Have disconnected the stepper motor connector and the engine revs as
> would be expected. It had occurred to me that the stepper motor might
[quoted text clipped - 3 lines]
> Cheers
> Geoff

Stepper motor problems are common with the V8s and can cause all sorts of
symptoms, including erratic idling. Remove the stepper motor and give it a
good clean inside. It costs nothing and it might give you a temporary
solution.

Signature

Rich B
Ducati GT1000
Take out the obvious to email me.

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GWGY - 30 Dec 2007 23:55 GMT

Have taken the stepper motor out and given it a good clean. That has
made no difference. Have blocked off the incoming pipes and it idles
OK (Base Idle??) Doesn't rev on start up either.

When I lay the stepper motor on top of the engine it can be seen to
move slightly in and out.

But by how much should it move in and out? This one moves no more that
1 cm outwards and then back in. Is this correct?

Cheers
Geoff

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GWGY - 28 Jan 2008 19:22 GMT

> Have taken the stepper motor out and given it a good clean. That has
> made no difference. Have blocked off the incoming pipes and it idles
[quoted text clipped - 8 lines]
> Cheers
> Geoff

Well finally solved the problem myself.

It was the stepper motor at fault.

Geoff

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