I'm working on a 4E definition.
About 50% of the time it idles about 1600 rpm after driving, and the iac hisses like its got a crazy vacuum leak. Iac at max steps which I have set to 75(for diagnosing problem). Then it will slowly come down to set rpm after a few minutes but the steps stay at max 75. Adjusted the iac and tps (was at .31, set to .54) per the sticky thread and that helped for about 10 minutes but then the the idle wouldn't come down at all. I unplugged the iac while running and plugged it back in and then the idle settled down and the steps came down. The problem repeats at random.
The last thing I did was let the steps come down to about 20 and I unplugged the iac, so far it runs great and acts like it should.
The iac is clean but I don't know how old. Is the iac bad? Or do I have a tuning issue. Any ideas would be appreciated.

 

Did you do the minimum air adjustment? I think theres a write up here for it. You papareclip the ALDL, turn on ignition but don't start engine. This will drive the IAC closed. Then unplug it. Start engine and set idle screw (Min Air Screw on EFI) to about 100 RPM less than desired idle in chip. Turn motor off, plug in IAC, clear codes and restart. I like IAC between 20 and 40.

Another issue I have seen is BB Chevy IAC has 2 wires crossed. If you did a conversion with BB harness or then used SB TBI this will cause IAC issues.

I know your close to CDA if you ever want to get together and work on it.

 

Yes I have done that procedure and it always stays at max steps. I tried it again just to verify and rpm is the same and also tps voltage. I drove it to work today with the iac unplugged and it ran great with the exception of the cold start needing throttle as expected. Is it possible the computer is not seeing the iac opening and commanding it max to compensate? Although it does have to open to go high idle right?

 

Just not sure how it could not see it and send it wide open.

Like I said I had this same issue because of big block wiring. May want to verify your IAC wires are correct for ECM used!

 

Since your playing with chips have you looked into the stall saver?

If the motor starts to stall it adds steps to IAC.

 

I'll get the diagram and check it tomorrow. It is a retrofit from a company in the midwest somewhere I think. Its actually on a 4.2 jeep yj.
I think your right that if it can command it, it has to be able to see it.
I drove it home after resetting the IAC and same thing, about ten minutes and it wont idle down, unplug it and runs fine but stays at full steps.
I looked through all the tables and cant find anything about a stall saver. Just a power steering cramp table. You might have to school me a bit.
Thanks so far, by the way I'm in IF.

 

Ok, I couldn't wait till tomorrow, I couldn't sleep until I figured this out.
I've made some progress. Wiring ok. Started thinking that the computer has to command max for a reason. Not enough air, right. I opened the throttle blades until the IAC steps started dropping. I monkeyed with the blades until I was at 20 or so steps at desired idle. Readjusted the TPS and raised the max steps to 150 (it should cold start better). The steps now go up and down to compensate like normal.
Duh, it always goes back to the basics doesn't it? Usually the problem is the doofus working on it.
But now I have one more problem. There isn't a transmission gear sensor, so the computer does't know which gear it's in (always drive). When I shift into reverse or drive it just about kills it (sometimes does). If it doesn't, then the idle slowly climbs to the normal idle (which I've moved as low as 700 up to 900). At 900 it slams into gear, but if you get it low enough to not slam it usually kills it.
My question is, do I need to add a gear sensor, and is there settings to adjust this?
Thanks again for the thoughts EagleMark. Any more thoughts?

 

In a conversion most guys don't bother with the Park/Drive switch but I have found it does help the transition. I think, remeber I think if you ground the P?D wire you will be better than nothing at all.

Also in a conversion a lot of guys leave out the VSS. I have found that the VSS will help create a more robust idle and have seen other drivebility improvments.

I just uploaded XDF and ADX files in our photo gallerey we have all been working on. Lots more IAC options then a stock $42. Look for the
Super_1227747_42.XDF and ADX
http://eagle-mark.com/pictures/index.php

I still think you have to register to get them but it's not hard.

 

Thanks for the help EagleMark. I'll try to talk the guy into adding the vss and gear selector. But until then I've got it at about as smooth a transition as I can and it seems to be running fine down the road, i.e, it idles down at stops and accelerates good.
Again thanks for the help, any more thoughts are always welcome.

 

Not really, gave you all I knew about the issue because I have done a lot of conversions and had these problems.

Maybe just give me a call next time and we will have a meeting of the minds over it? I know your close to me in CDA. I like to work on the hard ones in person and always learn from others and pass along what I have. Good Luck and God Bless!