ilde surging, need help!!!!!

i just bought a 92 talon tsi. i bought the car knowing that it did not idle right, but it only had 95,000 miles on it and it was only $2,400. when i got it it surged from aobut 1200 to 1800. i went ahead and looked at the BISS, it was really loose so i tightend it. no leaking what so ever, now only surges from 1200 to 1400. need help, dont know what else to do