Car hesitating and low revs

Hi all, just a quick question. What would cause a 620 auto to hesitate when pulling off?



I was at a roundabout earlier and went to pull off when I saw a reasonable gap. The car seemed like it had died for a second or two then the revs shot up and it pulled off as normal.



Obviously I nearly got hit by another car due to the hesitation, so I want to sort this as quickly as possible.



The revs do seem to be a little on the low side while idling in traffic, probably about 600rpm, but when the car is in park they are around 900.



Any help greatly appreciated.

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