First tune assistance ;-)

Thank you in advance for assistance!

Working on a 91 chev 350 with 1227747. Finally got it up and running with no error codes from SES and emulating from autoprom. Loaded the ADSU bin from here and tweaked a little for EGR, ESC, TCC etc.

A challenge I'm having is I can't get the thing to idle below 1000 rpm. We set the IAC a few times and the darn thing won't drop the rpm when it's hooked back up. We set it to right around 60. We took it for a quick test drive and upon returning the idle was at 2000 rpm w/IAC open at 145. It stuck there for 30 seconds or more then I could see the IAC counts dropping to about 18 and the idle drop to just under 1000. Then it raised the IAC to get the damn thing back to 1000.

I ave been playing with IAC - Desired C/L Idle speed and I don't get any change at idle. I have all RPM fields set to 600. Also, we installed a switch to the A/C input to the ECM for a high idle trigger, played with that too and didn't get any response.

Any ideas?

How are you adjusting the IAC??

If you are using TunerPro, use it to adjust the IAC.

After the motor is completely warmed up just turn the the throttle stop screw (in clockwise if counts are too high or out counter clockwise if the counts are too low) about a ¼ of a turn at a time while it is running then shut it off so that the ECM can reset. Then restart the motor and after the motor idles down look at TunerPro to see what the IAC count is. If it is still too high, keep repeating until you can get the count below 20 (I always shot for 10).

If the motor is still idling high you need to look for other problems (throttle linkage, vacuum leaks)

However I bet this is the problem: if you are using a an ALDL cable with the 10k resistor in it will cause it to idle up any time the cable is hooked up. You do not need the 10k resistor. I had the same issue, I was able to overcome the high idle issue by pulling the A wire (ground wire) out of the ALDL connector under the dash. I have been data logging just fine ever since without have it go into ALDL mode and idling up.

As far as using the A/C trigger wire for a high idle, it can be done but it is a little more involved and requires some additional tuning to make it work. Maybe when Mark gets back he can assist you with this issue.

IAC logic is completely different in P/N or D/R. So after a drive shot for 10-20 IAC counts in drive, then when you go to neutral IAC will be lower and RPM higher.

You'll never have the Desired Idle RPM setting in Park/Neutral. It will always be higher.

You can lower this somewhat but to low causes issue. Look at these two settings to 850? Last time I tested lower then that weird things happened?
"IAC - Max RPM hot Pk/N"
"IAC - Max Cold RPM in Kickdown Mode"

Devind was on it. I had the 10k switch on and that put it in ALDL mode and idled at 1000. Moved the switch to the outboard position, turning off aldl mode, and my adjustments were working and idle came down to 600. I also found "IAC - Idle RPM For C/L ALDL" that adjusted the idle with the 10k switch on. I think it still works logging data with the switch off too.