I have a 1996 306 xsi and the oil gauge has recently started to give irratic readings. This morning it deteriorated considerably & on start up it went right over past the maximum 8bar mark and gradually came down as the engine warmed up. After 10 minutes, it was bobbing between 0-1bar when revs were up & showing nothing at all at idle. Checked the oil levels & all are fine, & there are no other warning lights or indications of problems. Any ideas?