OK i have an mx3, with the 1.8 V6 k series motor. And i ahve the 2.5 klze in it now. (so i know alil bit)

When i use to have idle probs it turn out to be these things:

TPS
Cracked airintake hose
Leaky throttle body gasket
iac
Coolant lines not connected to the throttle body (coolant bypass mod)
stuck throttle cable( stuck liek a milimeter open idles at liek 2000 rpm)
Vacume leakes, but that usually cause ur car to die...
mis adjusted idle screw on the throttle body.
missing fuelinjector sealing ring(caused it to idle craptastic)