IAC Duty Cycle not working in S300

[blacksi76]

2000 Civic SI, H22 Turbo
Hondata S300
Golden Eagle Intake manifold
BDL 72mm throttle body

Since installing my new motor last fall I had trouble starting my car after I had it tuned, then my tuner fixed the starting tables in S300 and not it starts good, but he also noticed that my IAC duty cycle was't working in S300, and he said that there was no air getting into my intake manifold through the IAC. When I cold start my car, the idle stays at like 6-700rpms and once fully warmed up, idles steady at 1000rpms. The IAC show open up and allow the car to idle up to 1300 at cold start and then slowly drop down to 1000 or whatever idle my tuner has set for my car to be at...

1) I swapped the IAC out for 3 different ones, and the car responsed the same. I also tested each IAC to see if the solenoid was working.
2) I checked the wiring on the IAC plug which has 2 wires, a yellow/black (12v ignition) and a black/blue ( ECU)...The yellow/black has power and from what I can tell the black blue works from the ECU as it worked before I installed the new motor and intake manifold etc...
3) I removed the throttle body and trimmed the gasket that was covering the hole orfice that air flows from IAC and that didn't make any difference either.
4) I also backed off the idle screw all the way out to let as much airflow into the throttle body I could, and that also didn;t make any difference. I figured the car would idle high so I could adjust the idle screw at cold start dolwn so whenit hit 1300rpm, then that was where it should be...cause the car does idle at 1000 when fully warmed up.

Any suggestions???

[Spunkster]

If you adjust the slider all the way from one side to the other in the idle control parameters does the idle change at all?

[blacksi76]

no, no change, thats whats making me think the IAC is not openning....thats what the tuner said too...what do you think?

[Spunkster]

Try the s300 in a different ECU, perhaps your ECU is damaged.

[blacksi76]

I don't have a spare ECU, could I send mine in to be checked over?

[Spunkster]

If the ECU is the problem the only option you have is to replace the ECU. The only other posibility is a wiring problem in your car. You can try the ECU in a known workign car and see if that works.

[blacksi76]

i will see what I can do, although my ECU is a Hondata prepared ECU, P28 with the OBD2B connector built in...its only a few years old...Would I bet better off using a P72?

[Spunkster]

You can use any compatible ECU you want, but you will need an adapter harness is if does not have the built in adapter.

[blacksi76]

yeah there's noone around here that has anything like that I could use....It would be easy enough for me to send my ECU in to be tested if thats possible..

[Spunkster]

It would be $50 to test the ECU, but the IACV cannot be tested on a bench. If the ECU is the problem we do not repair ECUs so you would still need to purchase a new ECU. I'm trying to help you prevent wasting money when you could determine the source of the problem without spending additional money.

You can even try it on a stock unmodified car and just upload a different calibration.

[blacksi76]

I just tested for continuity from the blackblue wire on the IAC plug to the ECU by disconnecting the ECU plug and used a multimeter set on ohms in the lowest setting and there IS electrical continuity in the IAC wires black/blue that goes direct to the ECU. And there is also 12v ignition power going to the yellow/black wire on the IAC plug so that rules out the wiring being stretched or broken in the harness.
I will start the car next and connect the IAC plug to my spare working IAC valves and adjust the IAC duty cycle slider in the S300, and see if it opens or closes the IAC by visual inspection.

[blacksi76]

I bolted my IAC last night to the intake manifold, and turned the ignition on, and when I did, the IAC started to make a high pitched electrical noise....I unplugged it and it went away, and plugged in a spare I have thats not bolted to the IM, and it made the same electrical noise....I plugged it back into the IAC on the IM and started the car and the car was idling very low again whenit was warming up, like barely enough to stay idling so I had to give it a little throttle to bring the rpm's up to 1200 till the motor warmed up a bit, then as it warmed up was idling at 950ish....So I wanted to check the IAC duty cycle slider in my S300 again to be sure cause last time it was completely unresponsive....This time, whenI moved the IAC slider all the way to the left and hit the upload button the IAC started making a very loud buzzing noise it didn't make before,and the idle did go down a bit, but not much..... I placed my hand on IAC and it was vibrating and VERY loud....so I moved the slider to the middle of the IAC duty cycle and hit upload and the loud buzzing stopped immediately and the idle came back up to 950ish.....When I moved thew IAC slider all the way to the right to max duty cycle....no change at all from normal.....

I did a professional smoke test on the motor as well, no leaks anywhere in the system to be causing a vaccum leak, so it seems as of now that the ECU and S300 are working to make the IAC duty cycle change, so maybe I have a blockage or restriction somewhere in between the BDL Throttle Body and the IAC....When I forst installed the new engine before I had it tuned last year, it idled super high around 1200-1300 rpms, and I remember having to block off the IAC intake nipple on the Golden Eagle IM and get it to idle lower and I adjusted the BDL throttle plate set screw to close up the throttle plate a little more to restrict airflow, and completely close off the idle screw in the throttle body.......Now I have the idle screw openned all the way, and still a low idle....so maybe I have to re-adjust the throttle plate set screw again...

[blacksi76]

Found the problem...Design flaw in the BDL throttle body....the IAC intake port on the throttle body is completely blocked off when mounted onto the Golden Eagle Intake Manifold....This is why the IAC is not getting any airflow And why the idle set screw does absolutely nothing to the idle when its all the way in or all the way out.....