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Hello!
I'm tuning a 5.7 Trans Am using 165 ECM with $12P software.
It has LT4 HOT cam (218*I/228*E duration, 0.492" lift I&E, 112* LSA, so quite mild one), corvette aluminium cylinder heads and Accel Super Ram intake. Automatic gearbox.

It drives pretty well, but I have problems getting idle to stabilize. In gear there's no problem, but in park the vacuum signal gets quite erratic with that big plenum intake. RPMs go up and down and it will sometimes stall.
There's a log of this happening, and used bin attached.
I have unplugged IAC and set spark advance to constant 30* and it still oscillates, meaning the problem lies in fueling. I tried using closed throttle VE table to elliminate erratic MAP and it is a little better, but still not acceptable.
I tried adjusting idle VE area, it is more stable when set VERY rich (not until about 12.5 AFR!), but that makes the car spit fuel out of tailpipe

Also, strange thing is that IAC will not try to adjust to demanded idle rpm. I have idle rpm set as 750, and it will keep the engine around 1000rpm with steady IAC counts...

Thanks for any help, as I have gave up for now.

Have you checked for vacuum leaks?

If you still have idle proportional spark active turn it off via it's temperature flag it's probably cycling idle timing up and down causing it to surge

No vacuum leaks. Max idle spark is set to 0 and spark advance is steady on the log. Only fueling goes up and down constantly.

Not triggering accell enrichment I'll get on the pc and check the logs

AE might be a good thought, I'll check it.

The log has spark advance oscillating, but after that I hardcoded it to 30* and improvement was minimal.

You are targeting 14.7:1 at idle in places it hits closed loop fueling and rpm swings with the 02 sensor swing.target a real idle number somewhere in the 13s and it will smooth out.youbalso have 2 error codes one for unstable coolant sensor volts and a/d channel error

Thanks. The errors are from APU emulator running. I always get them when I use emulator instead of normal EEPROM.
Why would it need such a rich idle? I've tuned a lot of LT1 engines with same cam ans similar heads, and they all idled well around 14:1 AFR.
Would a bigger intake and older ECM make such a big difference?

Another thing, there are no parameters in 12P to control IAC PID regulation. Is there an XDF with those available?

Generally I have found all engines I have tuned like AFR for idle to be around 13 to 13.5.
14 can work but at that and high AFR I find the engines looses vacuum (loss of torque) and the ignition becomes unstable as in there is a lot of misfires due to the very low cylinder charge density and at that low density what might seem rich in figures behaves much more like a lean condition.

So basically the engine runs unstable and pops a lot from the exhaust and generally stumbles around at idle.

Best way to know if you get a good AFR is to use the monitor trace and watch the Kpa, change the target AFR each way and watch, you want the lowest vac but the leanest of that plateau area of AFR rages used to get the lowest vac.

Exact same with timing, least advance of the highest vac plateau area.

Hope that helps.

In 12p you dont set set iac pid for idle, you set idle rpm and let the ecu detect idle to target it. Most iac settings are in steps for various things.