my car keeps stalling itself when i come to a stop at a junction, not allll the time. like 2-3 times in a journey. but other times it drops to 500rpm.

It's a Ford Fiesta LX Mk3 1.3 M Reg

It only happens when the clutch is down, not in neutral. It's starting to piss me off. What could be causing this?

any other information needed please feel free to ask.

Cheers.