How about first checking engine temp to see if there is a problem with the thermostat, ECT, etc?? Idle is a symptom of another issue, and not the issue itself. 16v's bog with vacuum leaks once the car is warmed up, as well. You should give info about what the car does from first start up, idle, how it drops, etc. And also what maintenance you have done - tune up, timing, cleaning EGR, etc., etc.
'91 Tracker 8V, 1.6L, 5 sp, 4wd, 2dr, conv, CAMI, horribly rusty
'97 Suzuki Vitara 8v, parts car - worth its weight in gold.....
'61 NSU Quickly - 150mpg