I have had problems with my D16Z1 idling since i've had the car, and since, I have done the following...
1. No CEL's...
2. Bleed Coolant
3. New TB, TPS, MAP, IAT, FITV, adjusted my idle screw to only have it idle at 800
the lowest it will "drop" while surging, and 1100 to be the lowest it will "stay" when it wants... Which is very random.
4. Checked all vacuum lines, coolant lines, and did the FITV trick...
5. And if the IACV can go "bad" without throwing a code, that is my last guess, because the car will idle high cold, as if my FITV is working, and when I touch my gas pedal, it will begin surging? Sometimes it will begin to idle high, 1000, but wont keep a constant "low"... Or atleast even a non- surging idle. Any help is greatly appreciated as I have been doing all I have been aware of. Thanks

 

I say clean/replace the iacv. you using an auto ECU? I was getting a surging idle when I was using and auto p13, switched over to a manual p13 and fixed the problem.

 

this is the exact same thing im going thru too. My car ran great until a couple nighst b4 and it started doing this surging bit on me. My car threw a cel for the tps so i changed out the tb. Nothing. Changed out cap and rotor. Nothing. Changed out the o2 sensor. Nothing.

When my car is surging, i can get the idle to stay pretty steady 1100-1200 by sitting still and letting out the clucth a little bit to load the engine and then the idle will stay at a the idle level, but as soon as i touch the gas pedal, it starts surging again.