My 1999 Plus 8 VDO exhibits the same symptoms in winter. I unplug it and unscrew the rear bezel and put it in the boiler cupboard for a day prior to MOT and that sorts it out if it's playing up.
2009 4/4 Henrietta 1999 Indigo Blue +8 2009 4/4 Sport Green prev 1993 Connaught Green +8 prev
