Xantia 2.0 - high/fluctuating revs problem

[GB]

Once the engine is fully warmed up, at idle, the revs sometimes increase up to 2000rpm for no apparent reason, and sometimes they just steadily fluctuate between 1000 and 1500rpm.

When the revs increase to around 2000rpm and I slightly tap the accelerator, the revs in turn go up to 2500rpm. Turning the aircon off actually causes the engine to rev higher.

Also, on a couple of occasions I also noticed the car to accelerate without me even touching the accellerator.

What's the most likely problem?


Cheers,
GB

[Mandrake]

I know exactly what you mean, my 2 litre 8 valve also does this occasionally, and I havn't found the problem yet...(sometimes it will wander up to 1300 rpm or so when hot and then drift back down to normal idle speed)

Aparently the two most common causes are an air leak in the inlet manifold causing the MAP sensor to be fooled, or a sticking idle stepper motor.

The 16v has different piping to the 8v but there is one small manifold hose on mine going to the butteryfly assembly that if I disconnect it the idle immedately jumps to 1500rpm or so...which I guess proves an air leak in the right place can cause it...

Regards,
Simon