[Gmecm] SER# 1227747 ACSU promID Idle Problems

[Jay Vessels]

Hi there!

> This is after I ground the diagnostic pins on the ALDL connector, wait 10
> seconds for the IAC motor to zero out, remove ground from ALDL and start
> engine.  

This may not be the same on all TBI systems, but I don't think that's 
the right procedure for your system.  Except for my '84 Cavalier (which 
used a rubber plug installed in the TBI) all of the ones I've tuned use 
a somewhat different procedure than you describe.

The difference from what you described is that you *don't* remove the 
ground from the ALDL port before starting.  Leave it there.  Otherwise, 
the ECM will try to control the idle, and you're fighting it with the 
throttle stop screw.

Essentially:
1)  Key off, jumper pins A&B on ALDL.
2)  Key on, adjust TPS to proper voltage (0.5V on the ones I've touched, 
yours may be different?)
2a)  You may want to unplug the IAC, ensuring the ECM doesn't move the 
IAC pintle, but leaving pins Z&B jumpered should do this.
3)  Start engine and let it stabilize.
4)  Adjust idle speed to spec.
5)  Readjust TPS to spec.
6)  Repeat 4 and 5 until both are satisfied.
7)  Shut engine off, remove jumper, and reconnect IAC if unplugged.

Jay Vessels
1982 Chevrolet S-10 Sport, 2.8V6 TBI
1984 Chevrolet S-10 Blazer Sport, 2.8V6 (TBI pending)