Been having a problem with my Escort where it suddenly refuses to idle smoothly. Revs drop down to a few hundred and keep fluctuating slightly rather than being stable. Pulling the choke out a little bit raises the RPM enough to prevent the engine from stalling, but doesn't stop the fluctuations. Before, this problem could be solved by revving the car quite a lot until it clears up. This doesn't seem to work anymore and the problem stays for longer, sometimes going away after a while on its own.
There don't seem to be any common conditions where this occurs, does anyone know what could be causing it? Carburettor related? Ignition? Any help would be greatly appreciated.