RB25 IAC Voltage Problem/AC Idle Up

[john89s13]

I have a 1989 S13 with an RB25DET. I'm a little stumped on this problem, and needing some input.

RB25DET
Greddy style intake
Q45 TB (set to .45V)
Top mount turbo
Stock injectors, stock ECU
Wiring specialties RB/S13 harness

It idles very rough on a cold start, as if the cold start system isn't functioning properly. It's also pegged out lean on my wideband on a cold start idle. Once it warms up after cruising for a bit, idle isn't rough anymore, but it idles high at about 12-1300 rpm's. AFR at 14.7-15. No matter where the IAC adjustment is set. Both plugs on the IAC (brown and purple) have ground and 12V at all times. (When key is in the on position/engine running.) I didn't think this was correct. I have recently cleaned the IAC, I know it's not stuck. I'm wanting to wire the A/C idle up, so I don't have to turn it off every time I come to a stop. Just needing to get past this problem first. FWIW, it's also very rich on decel. I didn't think this was right either, I was under the impression that the ECU cut fuel on deceleration. Thanks for any input, much appreciated!

[rastaman]

I can't get my idle up to work when AC is on also. Idle drops to 600 when AC is on and voltage drops to 12v on battery..I did the same as you cleaned and adjust iacv. I'm replacing it tomorrow will up date let you know.

[john89s13]

Sweet, thanks! Hope it works.

[dbeiler]

Widebands usually display full lean (22) or full rich (7.5) until start-up/warm-up is complete. My RB25 idle speed changed when I switched from stock intake to a GReddy/Q45 setup. I even used the original IAC and made zero adjustments. It never idles under a 1000 anymore. The Q45 throttle bodies are notorious for sticking partly open. Physically push the throttle completely shut and see if the idle drops. Also make sure the throttle body vacuum nipples are completely sealed off.

[rastaman]

I have the greddy and q45 tb and it idles at 1k when cold and drops to 9k..op did you relean your idle? Disconnected tps when car is warm and adjust idle screw to where you want then plug tps back in while car is running..

[john89s13]

Nope, I didn't re-learn the idle. Completely forgot about that. I'm putting the stock throttle body back on at the moment to see if it makes a difference. Thanks guys!

[john89s13]

I put the stock throttle body back on, using the Greddy adapter. Re-learned the idle to 900. It made a world of difference. Cold start functions correctly, and the idle is rock solid. AFR's are back to the way they should be. A/C even works during stop and go better. The throttle response is also way smoother. Best de-mod I ever made lol.

I re-o-ringed the Q45 throttle body, so I know it wasn't leaking. My motor just didn't like it I guess. Maybe I'll figure it out later on.

[rastaman]

Hey did you ever get your idle to go higher when you turn your AC on? Can't get mine to idle any higher. I changed the idea up slionoide with the purple plug and no luck..I have greddy intake and q45 tb. Seem like when there is a load of any sort the idle drops.

[john89s13]

I never got the idle up working. I was confused about it, because both plugs on my IAC already have 12V at all times. However, I can cruise with the AC on now that I have the stock throttle body back on. It seems to be affected WAY less by a load than with the Q45. Mine would never idle right with the Q45. Even the power steering would knock it down a few rpm's.

[supersayianjim]

so o.p. how do you have the purple plug plugged up?? I don't have that on my setup and the car runs just fine. try unplugging the purple one and see what happens?? also if you need another iaac for sale(more than one).

[john89s13]

I have the purple plug on my harness plugged into the purple plug on my IAC. I know there isn't anything wrong with the IAC itself, just wondering why it has constant 12V at the purple plug.

[rastaman]

My purple plug only sees 12v when AC is on..it still don't idle up when AC is on..it drops.

[john89s13]

Yea, I'm lost on this one. Someone that's won this battle will have to chime in. Mine will be even more difficult, because I wired it myself with an external switch. The AC button on my control head is bad.