So being the naughty boy i am

i decided to take the golf out for a spin (with no tax as waiting for the log books still), you know just to keep everything moving etc etc. Dropped the other half off at work and went down some country roads to open her up. Everything is fine and it pulls strong in every gear and i was smiling all the way round. I do have a question though, the car seems to idle up and down when i pulled up to some junctions. Got to the first and it sat nicely then came to another one and it was reving up and down but still drove fine and pulled strong, pulled over in a lay by and it was idling fine again, next juction up and down again?

is it the throttle being a bit sticky or can anyone advice me where else to have a look? o yeah got it home and it was idling ok again? Bit confused.