Miss fire low revs

[meganfreeman]

Hi all, my car has just develpoed a miss fire on tick over and up to 1500 rpm. It still goes well but it sound like its firing on only 5 cylinders.

Last week the oil seperator was changed and the small valve behind the passanger seat (on engine block).

This firing on 5 cylinders happened before some 2 years ago when i first bought the car. A single plug was changed. Car only does 5k per year, should plugs go that quick, is it linked to the oil seperator. Any ideas guys.

Thanks

Megan