ODD Power Passenger Window!

I have a wierd passenger window on my 05 XJ8 VP. The glass will go up/down perfectly with the ignition in aux. With the car running, it will go up/down in spurts. I have to keep using the switch to even make it move a little up or down. I have reprogrammed it (holding the switch a few seconds up and down) after starting the car, but no difference. I replaced the driver’s main switch with no joy. It does the same with the single passenger door switch. All the other windows work perfectly.

Any ideas much appreciated.