Mk7 idle rev blip every 3 seconds or so

[aseriestipper]

Hi, I have been to look at a 2.4 2008 transit with 80k on the clock, it runs and drives sweet as a nut but I noticed a tiny dip in revs on idle about every 3-4 seconds which sometimes dissapeared. When cold the rev needle dropped about 2 mm and when warmed up the rev drop could be heard but no drop on the rev meter, it is a tiny blip not a big drop and I was just wondering what it migh be before buying. Thnaks for any advice

[Altransit]

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