Idle Set Up (93 & Older)

/ / Tuning Information and Common Questions

Idle Setup (93 & Older)

No aftermarket throttle body should be expected to work out of the box. Also, if you have a large cam and/or more displacement you should pay close attention.  All GM vehicles in our focus use what is called a IAC motor.  This motor controls a air bypass in the throttle body which basically controls your idle. For example, if your idle is low and needs to be raised the motor will open a valve and give the engine more air which will allow the idle to come up.  The IAC motor has a certain range it may operate in, officially its 0 – 160 IAC counts.  If the valve is closed completely it will be at 0 counts, open is 160.

What you want to do is set your throttle body up so that you put your IAC motor in a good effective range so that it may catch any idle dips and trim high idles just like it does in a factory vehicle.   To do this open your scanner and look for IAC counts.  With a fully warmed engine at idle in P/N we recommend 30-50 counts.  The closer to 30 the better but don’t drive yourself crazy finding it, after all that is what the IAC is for anyway. If your IAC counts are not in this area adjust your throttle stop until it does.  If your IAC counts are high add throttle stop (make blades open).  If your IAC counts are too low remove throttle stop.  All aftermarket LT1/TPI throttle bodies are adjustable. Stock throttle bodies are adjustable as well after you knock out the plug. The Computer will see that the TPS voltage is increasing as you adjust up. This may lead the computer to believe that you are intentionally holding the gas open so at this point it will kick the idle up under throttle follower and throttle cracker routines.  BE SURE that your throttle position (%) is zero before noting IAC position and making a subsequent change. You can reset your throttle position % by resetting the ECM, unplug battery, pull ECM fuse, etc.

After you set your throttle stop look to see if your throttle position sensor is still within range.  We recommend about .65 volts or so. An acceptable range is .5v-.69v. If you are outside this range elongate or slot the TPS mounting holes so that you can “clock” it until you get the appropriate voltage.

Here is a snapshot of a vehicle with a improperly setup throttle body.  Red stars have been added next to important data to help  you find them.