Strange issue with IAC counts and RAF

[3strokeEngine]

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.

[Ben Charles]

Sounds like you have an issue with fuel..

[3strokeEngine]

It idles at a 14.7:1 to 14.0:1 air fuel ratio in open loop speed density and runs fantastic so I doubt its a fueling issue.

if i go into the scanner and commanded the IAC counts to 160 it idles fine. Also if i reEnable the adaptive idle it will idle fine once the adaptive idle routines catch up. For what ever reason something in the tune is causing the IAC counts to drop and adjusting base running airflow makes no difference.

I just got off work so i have a chance to upload the tune

[3strokeEngine]

Anybody want to chime in on this? Base running airflow has no effect on IAC counts. Seems like an issue with HPtuners and this ECU....

[Russ K]

You need to adjust the throttle stop screw to get the IAC to 20-40 at hot idle in park. The Base Running Airflow doesn't affect the IAC counts.

Russ Kemp

[3strokeEngine]

You need to adjust the throttle stop screw to get the IAC to 20-40 at hot idle in park. The Base Running Airflow doesn't affect the IAC counts.

Russ Kemp

Well my TPS voltage is already around 0.65v at idle so i wouldnt want to open the throttle screw much more right? I suppose i could drill a hole in the throttle body but thats a last resort.

I dont get why i can't command around 160 iac counts in gear with out adaptive idle. I was under the impression base running airflow was translated into IAC steps in the IAC steps vs. %Flow table and the adaptive idle routines started from that point.

If i could command a 160 IAC steps at idle in gear it would be fine but for what ever reason IAC counts always drop to the 90-100 range and it idles bad.

So what table is it exactly that sets the "base" IAC steps for running in gear/park?

[Russ K]

Well my TPS voltage is already around 0.65v at idle so i wouldnt want to open the throttle screw much more right? I suppose i could drill a hole in the throttle body but thats a last resort.

Then modify the TPS sensor to make it adjustable.

I dont get why i can't command around 160 iac counts in gear with out adaptive idle. I was under the impression base running airflow was translated into IAC steps in the IAC steps vs. %Flow table and the adaptive idle routines started from that point.

I never disable the adaptive idle when tuning. The Base Running Airflow is the base position of the IAC before any adaptives.

So what table is it exactly that sets the "base" IAC steps for running in gear/park?

The opening of the throttle blade.

Russ Kemp

[3strokeEngine]

I never disable the adaptive idle when tuning. The Base Running Airflow is the base position of the IAC before any adaptives.

Russ Kemp

Right, and shouldnt the base position be as close as possible to the required running airflow with out the adaptives so that once reenabled the adaptives arent maxing out?

I would love to tune this with STIT(proportional airflow) and LTIT (Intergral airflow) but with these 1998 PCMs its not a loggable PID in the scanner with HPtuners.

How should i tune this with out having access to STIT/LTIT?

[3strokeEngine]

Anymore help would be greatly appreciated...