Xantia petrol engine revs won't drop

[Downunder]

When driving along at constant speed and then taking foot off accelerator the engine maintains revs and then suddenly drops. This gives a jerky action.
I have thoroughly cleaned the air intake around the butterfly with carbi cleaner.

Could it be the idle stepper motor. Someone has suggested the throttle position sensor. Where is this unit and how does it operate? Not much about it in the Haynes manual.

Would appreciate your input.

[xantia_v6]

On a petrol engine, idle/no-load speed is almost entirely governed by the amount of air getting into the manifold. So you are effectively looking for an air leak that re-seals itself some time after you have taken your foot off the accelerator.

My guess would be a binding accelerator cable.

[Xaccers]

The cables do eventually fray and stick until snapping.
Had it happen twice on Cassy.
If memory serves it was £36 for the cable kit, so after the replacement broke within 6 months I thought stuff that and went to my local cycle shop.
They sold a bike gear cable that had a metal block on it the same small size as the Xantia's accelerator cable for under £3.
Whipped out the clip from the pedal, pulled out the not so old but overpriced broken cable and threaded through the new bike gear cable.
Used pliers to fit the end in the plastic pedal clip and tied up the excess cable by the throttle (if you cut it off, it frays and shortens it's life).
This was on a diesel though, can't remember the cable layout on yours.

[Downunder]

Zac
I would have thought that the spring on the cam would have overcome any fraying in the cable.

Still I bow to your greater experience in these matters and shall inspect at the weekend if it stops raining - like UK here for past few months although not as cold of course.

I shall report back in case others have this problem.

[Xaccers]

If you can disconnect the cable from the cam and manually operate the cam, that will exclude the cable from the equation