Engine jumping/kangarooing

[Willw2k9]

Hi all

My polo has developed an issue with kangarooing/ jumping. It was described by my partner as 'rubber banding'. It will happen whether the engine is warm or cold, and will usually become apparent in second gear but will travel up through all gears. It gets so violent sometimes I worry the car will break down. You can tell when its going to start because the car gets sluggish. It started around a month ago, and I thought maybe a bit of sludge had worked through the fuel system as it was quite empty before I filled up, especially as the car is a 53 plate. The weird part is it doesn't do it all the time, and can go a week without. It was doing it yesterday right till I got on my drive, then when I took the car back out an hour later it was running fine again.

I've had the car on a diagnostics machine and it found nothing. The car has covered about 116000 miles. I also don't know if it's related, but my fuel economy is atrocious for a 1.2. I worked out yesterday I'm only getting 29 MPG (£30-40 a week) combined which I think is pap, considering I've had a 1.2 before and was only putting £15 a week in covering similar distance.

The engine revs stick when the jumping is happening, and don't seem to move with the problem if that makes sense.

I was reading a post on here wirh a similar problem and someone suggested air getting in somewhere? Would that cause it?

Thanks for your help!