Ford idle air bypass
Last Updated on July 23, 2024 by Mutiara
This device is referred to by many names, such as: Idle Air Bypass, Idle Air Control, Idle Speed Control, Throttle Bypass Air, Idle Bypass, Inlet Air Controller, Inlet Air Bypass, Intake Air Bypass, and Intake Air Control. The most popular being Idle Air Control (IAC).
The IAB mounts on the side of the throttle body. Air is allowed in from in front of the closed throttle body, and bypasses the throttle body plate. The air is then released into the open intake track flowing directly to the cylinders. The principal is providing the EEC with the ability to provide air to the engine without depending on the driver. The IAB isn’t capable of opening half way, it either opens or closes completely. The EEC sends many pulses per second to flutter the IAB open and closed. In a proper functioning state it flutters so fast that no changes in RPMs should be noticeable. This fluttering is called duty cycle, when it’s calculated a percentage of on time. So when the IAB is off it is at 0%, when it is fully open it is at 100%, and any RPM in-between.
There are 3 main needs for the IAB, while the fourth is debatable.
Starting
- The engine requires an unrestricted amount of air to start, so EEC opens the IAB 100%.
- As soon as the engine RPM self sustains and begins to stabilize we now need air to Idle.
Idle
- Idle is more complicated than the word implies.
- Idle needs to be smooth and stable.
- Idle is increased if the engine is cold to help warm up.
- Idle is increased if the engine is overheating.
- This increases the speed of the water pump to flow more coolant to the engine and radiator.
- This speeds up the speed of the radiator fan improving cooling.
- Idle is increased if there is a high load on the alternator.
- Idle is increased if there is a pressure spike in the power steering.
Deceleration
- When you take you foot of the pedal the IAB is at 100% to prevent stalling.
- As the engine returns to idle speeds the IAB lowers the duty cycle to keep the RPM stable.
- When the vehicle comes to a stop the IAB is now controlling the Idle.
Full Throttle
- The IAB does opens 100% at full throttle. But the debate is if air flow increases.
- Air now has the option to entering the full open throttle body or the IAB.
- Air diverting through the IAB would disrupt the main air flow path through the throttle body.
- There isn’t any flow bench data to support or disprove this.
- There is a possibility of higher flow, but it’s more violent and turbulent now.
IAB Testing
This is really easy to test. First as with all problems the trouble-codes should be gathered from the computer. If a code for the IAB is set off then the vehicle should be turned on and the engine brought up to operating temperature. The engine should be left to idle without any driver input. While the engine is idling, the IAB connector should be unplugged. If the engine begins to stumble or stalls the IAB is functional and does not require replacement. If the engine idle does not change the IAB should be removed for inspection.
The IAB can pass and still need repair, or it can fail and not need replacing. The plunger and internal spring can get clogged with dirt and oil. This will slow down the air flow and not allow the IAB to function properly. The best way to clean the IAB is to remove it and spray the internals with carburator cleaner. However if the internal solenoid is faulty the IAB will require replacement.
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Article & images courtesy of fordfuelinjection.com.
