I had what sounds like a similar problem a while back.
After advice from the Forum I cleaned out the Idle Control Valve (Rimmers do a kit with new plastic bits and a gasket, about £12 I think), but it did not solve the problem. It turned out to be a simple mechanical issue with the plastic thingy on the end of the throttle cable sticking a bit and not releasing properly at idle, which was why the problem seemed to clear with a throttle pedal blip.
Anyway, read all about it here, especially Post #15
https://the75andztclub.co.uk/forum/s...d.php?t=302496