I was having the same idle problem you are describing. I went through the whole, timing, IACV, FIV, vac leak test routine and turned up with nothing. I decided to chnage the 02 because it was old and I probably needed one. To my surprise it fixed it.
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sounds like an easy thing to try.. any1 got an o2 for cheap??

 

Hmmm..I have one form my Civic. Not sure if it will work for you? It's a four wire.
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nope im a 4g -----, 1 wire for me.... dustin says he can get one for 26 $!? (typo?)

 

Yeah, I read that also. I guess I got raped on mine because I know I paid a lot more than that.
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I was having the same problems.Idle was loping between 600 and 900 rpm at idle.

What I did was disconnect the A.I.C.V and with it disconnected I turned the screw on the T.B till it was at 500RPM.When I pluged it back in it was sitting steady at 600rpm.Havent had a problem since.

 

tried that I think either my iacv is dead. the alternator load signal is messed or the iacv is too dirty to flow enough air under elec load.

 

clean the IACV with Carb Cleaner or Seafoam, just let it soak for a while, reset the ECU and start her back up. If not, you can get an O2 on oxygensensors.com for $20, I checked earlier today, it's not a bad thing to have a fresh one anyway.

I did have an FIV go bad recently, luckily I too had a spare, the thing got stuck open and my idle was at like 2k, which sucks when you've got a loud exhaust. I'm switching to a B16 TB with no FIV, and then no more worries. I've got a few spare 02 sensors if you want to try a cheaper one, but you'd be better off with a new one.

 

My idle is screwed up also. I have a black top DOHC ZC in my 91 rex. It goes from 1500 to about 600 and back and forth once the car is fully warmed up. I tried looking for a vacuum leak using carb cleaner. I didnt find anything. I replaced the tb gasket anyway. I cleaned the iacv with carb cleaner. But mine doesnt have a screen in it. Either did my friends on his sohc zc. Is that normal. When i unplugged the iacv the problem went away. Does that mean that piece is fine or broken. I still have to try the FIV thing. I also bought a new O2 sensor but couldnt put it on cause it started raining. Im so sick of the up and down idle.

 

if and when u unplug the iacv the car idles perfect i'd think it was bad. when IACV's go bad then cycle. open closed, open closed.