My rpm yesterday started dropping down from 600 then surging up to 1000 and kept doing it at a stop.
I suspect either the power steering pump or the ac compressor is causing the belt to be slowed and the engine to surge.
It was a particularly hot day and the car had been running at 80mph for 30+ minutes with the AC on max.
The odd thing is this behavior didn't begin until the car was parked in the driveway for 5-10 minutes and then restarted and driven through town at under 40mph for 5-10 minutes.

Any ideas gents?

Thanks

 

Possible vacuum leak.

Lots of info here:https://www.jaguarforums.com/forum/tags/surges/

 

Thank you for the link, however it appears that most of those results are not pertinent to the x350 and of the two that were, symptoms did not match what is going on with mine.

This issue is intermittent and can be cured by turning off the air conditioning. Would a vac leak come and go? Would it exhibit no check engine lights or any other errors?

Thanks

 

My guess is that the amber engine malfunction light is coming on also so I suspect that your engine may have an intermittent miss. If that's the case, you will probably need a code reader to determine which cylinder is faulting.

 

There has been no check engine light.

 

Personally, if the problem can be cured by switching the AC off, then I suppose I would be bringing the car over to an AC specialist for service.