mk3 16V HELP!!.....please

[isitdead?]

Hi, would be very greatfull if someone could tell me how to fix the problem with my 96 16v mk3, brought it a few months back 45k with full VWSH! problem is that it idles eratically 99% of the time , and generally between 2800/4000RPM its as rough as a badgers arse (jults back and forth, shaken etc.) only when you wind it up beyond that does it smooth out. Makes driven a chore and the Hitecs @ VW havent an answer tho it says there is a problem with the air intake sensor which has since been replaced but still the fault reads? previous sensor melted right out? by the way i have replaced all ht leads and plugs, NOTHIN. PS. when i bought the car it was fine all i have done is a little hard drivin 4 bout 5K, are the 16V bad news?