2001 Volkswagen GTI running issues

My 2001 mk4 golf gti has a problem which has baffled a few different mechanics. Basically when I go to or over 80mph, afterwards I find that when I slow down to a stop the revs drop very low (on the verge of stalling) and the revs are bouncing around and make it hard, sometimes impossible to pull away; sometimes i'll have my foot to the floor and there will be no power at all, then after a few seconds it'll suddenly bounce back up and rev high and i'll bunny hop away. It sounds like its coughing and spluttering. I've found that I can sometimes clear the problem by revving it really high and hard, sometimes sorting the problem straight away othertimes it takes a lot of attempts. Any ideas on what could be causing the problem would be greatly appreciated as its getting to the point where its not only embarrassing but dangerous as well. Thanks.