I had a similar experience with my 307 hdi. If its anything like the same I
recommend you get it checked out.pronto!

On mine the rev display feeds off the cam shaft sensor in the rocker cover.
(mine had been disturbed during a service and put back in off centre)

Within a week the car wouldnt start and I had to get the car recovered and
the sensor replaced to fix the problem.  I was told that they have been
known to keep working for quite a while before total failure, so you might
be on borrowed time.

I'm sure someone on the group can tell you if it works the same in your
model.

Good luck.