Hi Guys,
It's been a while since I've been on here but I experienced some issues recently on a few cars where they seem to behave with an odd idle, and I wanted to collect some information on understanding the closed loop idle on the Mustangs and how to tune it properly, if possible.
For instance, what exactly controls the closed loop idle, what tables give the guidelines for it to follow. Setting a setpoint for the idle obviously controls which RPM targeted, but what controls the throttle blade to maintain a position and what adjusts the timing to stabilize the idle?
There are a few tables in question (2017 Mustang GT w/ MT-82):
Idle Airflow > ETC Idle Throttle Angle: The table reads airmass vs throttle angle. Assuming that this is a given airmass window to have an expected throttle angle for the airmass. Does adjusting it actually do anything?
Idle > Torque > Feedback, Proportional, Integral, Idle Torque Reserve, Decel Torque: Assuming the torque based PCM gives an allowable/ expected torque target at idle, and it uses this and the ETC Idle Throttle Angle to control the closed loop idle?
Issues Experienced Recently:
I have seen a few cars, after some modifications are performed, that seem to have some difficulty with the closed loop idle. Idle rpm targets usually are bumped for the modifications to aid the closed loop idle, but what seems to be reoccuring (Not all cars, two cars with the same mods, one will have issue and another won't) is the idle will increase and decrease rpm while sitting still idling. Spark advance would be ideal to remain at 12-18 degrees, however the spark advance will remain constant at the desired amounts, then increase somewhere to the neighborhood of 40-42 degrees of spark advance. When this occurs the idle drops with it, taking the trims with it. It will consistently increase and decrease timing, what appears to be hunting. When this occurs the idle drops and then increases back up, in some cases it attempts to stall out the car.
99% of the cars I've seen that this happens, timing hunts but the idle remains +/- 50 rpms on target and the timing jumps just makes the exhaust sound a little funny. However, the car I dialed in yesterday, would almost stall most of the time and in some cases, would actually stall out. I attempted lower rpm targets and higher rpm targets, adjusted the ETC Idle Throttle Angle table slightly closer to the airflow it was seeing, nothing mattered.
I'd like to understand how the system works so that I can fix it if this ever occurs again and moving forward to make sure these cars remain with good idle quality, as this is literally the first thing people experience when starting up their vehicle, not a good first impression if it has issues.
Kris