How To: Set Your IAC for Proper Start-up!

Howdy, Aces people! Today we’re going over a simple issue that can easily scuttle your start-up: Idle Air Control (IAC).

The vast majority of fuel injection systems that use throttle bodies have a valve that controls idle air, or how much air passes by the butterfly valve when the throttle is fully closed. This IAC valve is controlled by the ECU, and determines how smooth the idle is, as well as how aggressively the car starts when the key is turned.

If your vehicle is idling rough or having difficulty starting, IAC may be at fault. If the IAC valve is metering air too aggressively, the air-fuel ratio at idle and startup may not be rich enough for smooth running.

How to Adjust the Throttle Shaft Adjust Screw

To compensate for an aggressive IAC, you must adjust the Throttle Shaft Adjust Screw on your throttle body. The screw should be located on or near the throttle lever, such as here on a Killshot 2:

1. Turn the screw once.
2. Zero out TPS through your Aces handheld. To do so, navigate to:
   Main Menu > Wizards > Zero TPS
   This ensures that the ECU understands that the throttle is not being depressed, despite the fact that the throttle plate(s) are slightly open. This step is crucial to avoid issues with the ECU’s calibration.
3. Repeat this process as many times as is necessary—turning the screw once and zeroing the TPS each time—until your idle is smooth and startup is easy.

If you’re looking for a video walkthrough, the guys just cooked one up! You can see that video tutorial here.

That’s all for now! Until next time, Happy Tuning!