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Fast idle on Disco V8

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

Reply to
GWGY
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Stepper motor?

Reply to
Rich B

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

Reply to
GWGY

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

GWGY wrote:

Reply to
max

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.

Reply to
Rich B

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

Reply to
GWGY

Well finally solved the problem myself.

It was the stepper motor at fault.

Geoff

Reply to
GWGY

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