306 XLd surging when at steady revs

[Orbit Motors]

Afternoon,

Bit of an unusual one - my 1995 306 1.9 NA diesel has a rather irritating quirk when at steady revs. To clarify, it idles perfectly, however in a scenario such as steady acceleration to keep the car at 30mph in 3rd, the car starts surging (that's the best way to describe it).

It doesn't lose acceleration, it doesn't appear to want to stall or anything similar. If you take your foot off the pedal it will still roll nice and smoothly, regardless of whether it is in gear or not.

There is an intermittent issue with the rev counter sometimes dropping its reading to zero but doesn't seem to correlate with this issue. Fuel filter was changed recently as part of the service I carried out but hasn't made any difference. Water in fuel light occasionally comes on however I didn't notice anything untoward when changing the filter.

Thanks in advance