[ChevyTech]

He is what I think.

As for the high idle I would try swapping the PROM and if that did not work I would swap the ECM. The system shows the high RPM but does not look to be sending a signal to close the IAC.

1450 RPM at closed throttle with coolant @186 is not a correction for low voltage. That being said the low voltage would bother me to the point I would be testing diodes in the alternator. Compare it to your other vehicles and see what you think.

As for the not running real smooth in the first post, I think there is a good chance this engine has heavy deposits on the valve steams. It is running cold now and my guess is the truck has not been driven hard most the years it has been around. I would use SeaFoam slowly pouring some down the TBI while holding the RPM up (do not liquid lock the engine) on a hot engine, let go of the throttle purposely stalling it and letting it soak 15 minutes. Then restart and pour some more down the TBI at while holding the RPMs up. But before that I would replace the thermostat with a new 195 degree STANT brand thermostat. These engines get heavy deposits in the head ports mostly on the valve streams and especially if they run cold.

I have written about SeaFoam before and it seems like the exact same product as General Motors Top Engine Cleaner we used at the dealer.

When you get it running at the correct RPM I would adjust the throttle stop screw (Minimum Air rate) using the IAC count after some drive time above 45 MPH so the system does a relearn on its own. Get it adjusted so the IAC count is about 20 with it idling nicely, with a fully warm engine, transmission in in park, all accessories off.

The BLM (Long term fuel trim) and INT (short term fuel trim) are not consistent. The relearn you did, and working with it could account for that.

Keep in mind the fact that you are connected to the ALDL can affect how it runs and the idle speed. Disconnect from the ALDL and drive it after you make changes. I have never used WinALDL and don't know if WinALDL will let you switch modes.

Here are the modes:
Normal (open) mode
Some (limited) data can be observed without changing the engine operating characteristics.

Data link (also called 10K or special) In this mode all obtainable data is readable.
10K mode affects:
Closed loop timers are bypassed
Distributor ignition (DI) is advanced
PNP restrictive functions are disabled
IAC controls engine idle to 1000 RPM + or – 50 RPM (if applicable)
On some engines the canister purge solenoid is enabled

Factory test Mode (backup or 3.9K)
In this mode the ECM is operating on the fuel back-up logic used to control fuel delivery if the ECM fails.

I don't want to drown you in to much information. Let me know what questions you have.