'98 1.4 16v behaving strangely..

[davor78]

I am new here but I hope someone can shed some light on this..
I have had my Polo for a few months it has 55k and a full VW service history.
However recently, whilst sitting stationary in traffic/parked the engine idling fine (I assume 900 - 950 r/min is fine?) It starting making a "burr-burr-burr-burr" noise! And you can actually feel the car shaking too. Its like the engine is overrevving or catching up....

It lasts at the most 10 seconds but does it fairly regularly and the rev counter doesn't seem to go up or down from what I can see.
The car aslo seems to be able to drive itself, if I'm in traffic going slow put it in 2nd gear (no gas pedal) and just use the clutch to pull the car along - does about 18mph - is that normal?? Or linked to my rev problem?

Thanks for your time and any help!!
NW