Hell yall im having a weird issue on a 1998 silverado with l31 vortec and the "blackbox" PCM.
Ive been trying to get my base running airflow tuned for the cam i got (zz4 cam). Unfortunately the PIDs are very sparse on these PCMs and i cant log short / long term idle trims so the only way to tune my idle airflow is by disabling all adaptive idle proportional and integral airflow adjustsments and all adaptive idle spark so i can get my idle tuned in then reenable once im done.
Heres my issue:
I set my in gear base running airflow to 40% and the IAC counts start around 160 and the truck idles great at the commanded 650 RPM idle. However the IAC counts drop after about 5 mims of run time (at same engine temp) to around 100 or so and the truck wants to die when its in gear and starts idling in the low 500 RPM range.
What in the world could be causing this? ALL adaptive idle is disabled in this tune including spark adapt.