1999 Jaguar XJ8 engine stall

Hi hope you can help - just recently my XJ8 stalls as soon as it fires up, even if the engine is hot from a previous journey. I need to press the accelorator pedal to try to keep it running but as soon as I take the pressure of the accelorator pedal the engine revs rise and fall erratically and the car stalls. This is intermittent as I could try again five minutes later and the car will start with no problem. Trouble is I have no confidence in taking the car on the road as the problem then returns and the care stalls at a junction.

Hope you can help - thanks alot