Idle Help!

[CSJTA]

I'll try to explain this the best I can. Having a hard time getting the idle down with my new camshaft. This cam has alot of duration and very little idle vacuum, about 6 inches. Anyhow, the only way I can get it to idle is run the throttle stop screw all the way out, actually opening the butterflies in the throttle body. Well of course when I do this, IAC counts go to 180, and I loose the abililty to control idle, it idles but I don't think the ecm can control the idle with the IAC counts like they are. I know there are no vacuum leaks, just wondering what this is telling me, being I have to open the throttle to get it to idle. Thanks, CJ. Oh, and I do run the FAST bank to bank.

 

[TurboJim]

Are you running it in closed loop at idle? You might try that, see what the corrections are doing, and adjust your VE table to reflect minimal correction. Then put it in open loop if open loop idle is your desire. Otherwise the low vacuum may be being seen as high load and the ECM is dumping fuel at it.

 

[CSJTA]

Running in closed loop idle presently, may have to try open loop. AE fuel vs map is zeroed out right now, so no enrichment from that at idle.

 

[bobc455]

What is your target idle speed? Where is it actually idling?

What is your target A/F ratio? Does this match the actualy A/F?

I don't understand what you said, when you screw the throttle stop screw all the way in, are you opening the blades or closing them? Are you having trouble getting enough air into the engine to idle, or is your idle speed too high and you can't get it down to what you want?

I wonder if your IAC is wired wrong, and when the ECU tells the IAC to close it's actually opening.

-Bob Cunningham
bobc@gnttype.org

 

[CSJTA]

Hey Bob, thanks for the reply. I'll try to explain a little better. When I turn the throttle screw all the way in, or open the throttle blades, this is when the car will idle. If I back off the screw, or close the throttle blades, the car will not idle, the idle speed is to low. When I do this, the IAC counts are maxed, about 180, and I loose the ability to control idle speed, it will idle at about 1200 rpm, no matter what I tell it to do, adjust idle speed up or down, it stays at 1200 rpm, so I assume the IAC has lost it's ability to control idle speed. Idle AFR is set at 13.5, if I richen the idle afr, it seems to idle worse. Watchin the o2 correction, it's pretty consistent at about 4 to 5 percent each way. Bob, it's almost like whatyou said, like it wants more air at idle. Well if the weather breaks a little this weekend, I guess I will try somethings and report back. Thanks for the help.

 

[bobc455]

Check to make sure that the IAC is doing what it's supposed to- 10 is closed, 180 is open.

1200 doesn't sound unreasonable for a cold engine, but it still seems like that when you close the throttle blades, the idle speed should go down.

Let us know what you find....

-Bob Cunningham
bobc@gnttype.org

 

[JrTuner]

A couple of questions for you. How is your setup wired? Is it the factory harness with a splice in adapter harness? If so whos harness is it? or is it a FAST harness. There has been a lot of confusion on IAC wiring especially when the newer flat four wire IAC is used.

 

[CSJTA]

The harness I use is the FAST harness, it uses an adapter to hook up the IAC, goes from square plug to flat plug. I believe it is wired correctly, reason behind that is because last year I ran it this way, and it worked fine. Only thing I have changed is the camshaft and headers from last year. Hopefully I can play with it some this weekend and see what happens. And Bob, when I close the throttle blades, the idle does go down, that's the problem, it's like the IAC won't move enough to make it idle. I have to open the throttle blades to make it idle, I have switched IAC motors also thinking it was a bad IAC, no difference.

 

[CSJTA]

Well looks like I got it fixed, the Holley throttle body I run doesn't have what I call an IAC bleed hole in it, so I drilled a hole like the Factory throttle bodies have, and idles well now. Thanks all for the help.