i have the same sort of problem on my 306 xsi 2.0.it has an electronic oil pressure switch. when i start car oil pressure could go to 8 bars then down to nothing some days it read 2 bars. i had the oil pressure check and it was ok 4 bars on idle going to 6 bars reving. this was a faulty switch which peugeot want forty five quid for one . as nobody else can supply a pattern part. have learned to ignore it now as if there was a problem the oil light would come on.
hope this helps
