Golf - Unstable idle

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Wed 27 Aug 2003 20:59
Golf - Unstable idle - John D
My MK4 Golf 1.6 has an unstable idle. It is at its worst when trying to fast-idle at 1,200rpm – it cycles between 1,000 and 2,000 revs with the throttle pedal “kicking” each time the revs reach 2,000.

I suspect the idle control valve may be faulty. Does anyone have any suggestions please?

The car is a 2000 W and has done 40,000 miles. It is an Auto.
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Thu 28 Aug 2003 00:03
Golf - Unstable idle - David Davies
Suggest you have the brake servo pipe(from inlet manifold to servo) checked for leakage.Very common on this model.
David Davies (Tune-Up Raglan)
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Fri 29 Aug 2003 17:04
Golf - Unstable idle - John D
Thanks David. I’ve had a really good look at this pipe today and it looks in good condition. I’ve not gone as far as disconnecting it & testing the non-return valve though.

The fault is getting worse, so hopefully should be easier to locate. This morning it was idling at 1,200 to 1,400 (a right pain for an auto!).

Interestingly, by disconnecting and reconnecting the small pipe from the inlet manifold to the oil breather (before the butterfly), the idle returns to about 850rpm and remains there until the throttle is opened.
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Fri 29 Aug 2003 22:01
Golf - Unstable idle - Halmer
I had the same problem with my 1.6 S Reg Golf.

It was cured by the first VW dealer by cleaning out a small sensor hole somewhere or other that gets full of carbon and crap(so they told me).

When the issue arose again some 12 mths later a different VW dealer told me that there was 'no such hole and the computer says that there is nothing wrong with the car'.

Not sure which was telling me porkies and which one was right (if any).

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Fri 29 Aug 2003 23:17
Golf - Unstable idle - David Davies
It sounds as if you may need to have the 'throttle adaptation' reset.This procedure is carried out with a scan tool after cleaning out the throttle body or fitting a new throttle body.You probably need specialist help with this problem and do not delay as the excessive engine speed could adversely affect the auto. transmission.
David Davies (Tune-Up Raglan)
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Sat 13 Sep 2003 22:40
Golf - Unstable idle - John D
Stop-Press latest! The car became undriveable – it wouldn’t run below 1,400rpm and then very lumpily.

The inlet manifold was full of oil, so I took it off and washed it in petrol.
The plugs were due for changing, so I fitted a new set.

On re-assembly the car ran perfectly, with the idle rock-steady at 800rpm.

My conclusion is that the oil in its bronchial tubes caused the symptoms. The jury is still out over whether overfilling was the root cause, or if I will get a recurrence.

Incidentally, I tried to read the fault codes by linking pins 5 & 6 of the diagnostic connector. Unlike my Dad’s Vectra, there is no light on the dash with which to read the codes. Can anybody tell me how to do it please?

With thanks again to Honest John and contributors.

John D
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