What should I do when my IAC valve is replaced?

Any time the IAC valve is replaced, this “learn” procedure should be performed. The throttle stop screw’s primary function is to prevent the throttle blade from closing too far and getting wedged/stuck in the throttle bore. However, it serves as a secondary function to adjust the minimum air setting.

How does the IAC affect air flow to the engine?

Typically as the IAC’s pintle extends, air flow to the engine is restricted as the air passage is shut off. As it retracts, air flow to the engine is increased as the air passage is opened up. This air passage is a simple bypass for incoming air to take around the throttle blade. Diagnosing problems associated with the IAC aren’t simple.

Why do aftermarket camshafts lower the vacuum level?

Aftermarket camshafts with lots of duration or lots of overlap tend to lower the amount of vacuum an engine can generate at idle. Lower vacuum levels translate to less pressure differential between the intake manifold and outside (ambient) air.

What happens when a TP sensor is out of adjustment?

If this sensor is out of adjustment or is failing, the result could be stalling, idle surge, flat throttle response, hesitation, or erratic engine operation. Most of the TP sensors you find on stock Fiero engines are the adjustable type while those found on newer GM engines are usually non-adjustable.

What does the throttle position sensor ( TPS ) do?

Throttle Position Sensor (TPS) The job of the TPS is to tell the computer what the position of the throttle is. This sensor is vital in helping the computer determine if the throttle is closed or open; or how fast the throttle is opened or closed.

What causes the vacuum level to drop at idle?

Engines that have higher compression or are new/rebuilt can have higher internal loads/friction which can also result in a drop of idle vacuum levels. Basically any condition that increases load on the engine will result in the vacuum level to drop at idle, which will require the IAC or throttle blade to be opened up to compensate.

Are there trouble codes associated with the TPS?

There are trouble codes that are associated with the TPS. One code will set if the TPS voltage is too high when the computer expects to see it lower. Another code will set if the TPS voltage is lower than the computer expects to see.

What’s the best way to test an IAC valve?

Without a doubt, using an OEM-level scan tool is the easiest way to test an IAC valve. OEM-level means the scanner has most of the same functions as the dealer’s factory tool. Code readers and OBD-II scan tools don’t have the necessary bi-directional controls to test an IAC.

Can a bad IAC cause a DTC to set?

If you do not hear a change in RPMs, do not assume the IAC is bad until you do further testing. Also, this test may cause DTCs to set. With the engine off, unplug the IAC. Then start the engine and listen for an idle speed that’s either too high, too low, or fluctuating.

How to test an idle air control valve?

How to Test an Idle Air Control Valve 1 Check for Diagnostic Trouble Codes (DTCs) Is there an idle speed or other IAC-related DTC stored? 2 Perform a Visual Inspection If you find IAC or idle speed codes stored, you can move on to performing a visual inspection. 3 Test the IAC Valve (Without an OEM-Level Scan Tool)

How to disconnect IAC valve from check engine light?

1 With the IAC valve connected, ground the diagnostic (ALDL) terminal (same as you would do to flash trouble codes thru the check engine light). 2 Turn ON the ignition, but do NOT start the engine. Wait at least 30 seconds. 3 With the ignition still on, disconnect the IAC electrical connector.

What should I do when my IAC valve is replaced?