TL;DR: The only airflow/fueling sensor this car has is MAP. No IAT. No MAF. No O2s. It won't idle properly (go figure). It's a straight piped 6.0 LQ9 with very low restriction intake and a cable actuated throttle and IAC (idle air control). I think the IAC tuning is both the problem and the solution, explained more below.
The car runs. I've been working on it over the last couple days trying to improve the drivability. Owner complained of frequent stalling. On idle (800 RPM), it was very rough and merely turning on the AC would stall it.
I fiddled with the idle PID settings and got it to maintain idle smoothly and more aggressively recover from RPM drops. I also dialed back the idle spark advance to 10, and 12 at 800 RPM and below, and roughly doubled the idle requested airflow. I also dropped the spark timing adjustment for idle overspeed and underspeed by about half so it wouldn't be reacting so fast. Currently, underspeed adds 12 degrees at -100 RPM relative to expected idle. With the current in-drive idle base spark set to 10-12 degrees, that would give it 22-24 degrees advance for idle recovery. Increased torque model of the AC. And lowered the engine's inertia model by 1/3. As of yesterday and this morning, that worked great. It would start up fine, idle fine, I could switch gears and screw with the AC and it would run great.
Now this afternoon in hot Florida, it usually stalls on start. It'll start, hit idle RPM for a split second, and then straight to stall. If it's idling on its own (with 0% throttle) after starting or while driving, it idles fine. PIDs seem to be good. However, in circumstances such as coming to an intersection and letting off the gas, it'll stall within a couple seconds. Sometimes it'll dip very low and recover. I have to keep my foot slightly on the gas to keep it from stalling and even after coming to a stop, with me needing to apply throttle, if I release the throttle, it'll stall. It can only maintain idle on its own after it's already had a moment to maintain itself.
I've tried boosting the throttle follower by 3x and I've tried enabling the throttle cracker but I couldn't tell a difference. And technically, when I first flashed the throttle cracker settings is when it started stalling all over the place but that was also several hours after the tests this morning and I flashed the previous version and it kept stalling anyway.
My hypotheses:
It was around 80F this morning and now it's 85F. The IAT is busted and giving crazy readings (which was largely why it had rough idle to begin with) so I flatted the entire IAT map to 120F. Maybe the temperature fluxuation is causing a problem.
The idle PID could be "learning" while the throttle is still pressed and when the throttle is fully released, the idle PID had incremented down too far and causing it to stall.
The IAC isn't opening enough when the engine is dropping RPMs (obviously) due to bad tuning. I don't think the IAC itself has an issue with how quickly it can open. I just cant figure out the proper settings to get it to idle properly.
I've attached the step 9 tune (the one used this morning where it ran fine, and then didn't run fine for the last couple hours).
I also attached two logs:
"Throttle Cracker Terrible Run" was a step 10 flash where I enabled the throttle cracker and started to experience the frequent stalling, removing it after.
"Still Stalling on the way home" was back to step 9.
Camaro Step 9.hpt Throttle Cracker Terrible Run.hpl Still Stalling on the way home.hpl
Any advice would be appreciated. This car is never going to run properly until it gets the sensors it needs... but it just needs to run "good enough" for now and that seems completely doable. I don't understand why it ran fine this morning and not now.