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My 6 speed C4 Coupe MY2000 is displaying strange idle speeds.

When driving I became aware whilst sitting at lights, the normal idle speed of around 700 rpm had risen to 1100 rpm. I "blipped" the accelerator and the needle returned to the normal position only to then steadily rise to 1100 once more.

on my drive way at home I started the car up to put it away in the garage, the revs stayed at the correct idle speed without increasing at all I reversed the car into the garage, came to a halt and the revs went to 1100. I raised the revs again whilst stationary and they returned to 700rpm and remained there. Completely baffled.

any ideas anyone

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Is the AC on? That will raise the idle about 200-300 RPM.

If not, try a bottle of fuel system cleaner (like Techron).

Dear Loren,

No AC not in use, I am aware of the slight rev rise when AC is on but this is far more pronounced and irregular.

I am gonna try the fuel system cleaning as you suggest.

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The answers to Lorens and RoShambo posts:

I have checked the hoses all apear fine and the battery has not been disconnected.

In the high Rev band there is no interruption of the revs so not typical of the MAF but if anyone has a differing view, I would like to hear it.

Interestingly I turned on the AC to see what effect that would have and it seems to have a very profound influence. The revs, as you would expect rise, once they go above 1250 the rev counter falls back to a normal setting - then rises again and the whole stupid process repeats it's self.

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if you can't find anything obvious, I'd hook the car up to a PST. Idle is controlled by the Motronic, and chance are that it's getting a wrong sensor signal from somewhere. As the problem is always around in idle it should be fairly easy to diagnose.

An iffy MAF usually manifests itself in a lumpy idle.



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