How to Replace the IAC on a 2003 F250 V10

The idle air control, or IAC on a 2003 Ford super duty F-250 with a V-10 is located on the side of the throttle body. Its purpose is to regulate the engine idle rpm by allowing a metered amount of air to bypass the throttle plate when the throttle is closed.

Servicing The IAC

In most cases, you can clean a sticking IAC by spraying the internal valve with carburetor cleaner. On the 2003 F-250's V-10 engine, however, the positioning of its seals prevents you from cleaning it without causing additional damage. If a problem exists with the IAC, it must be replaced.

Symptoms of a Failing IAC

A surging of the F-250's engine at an idle is indicative of a fouled IAC. Carbon infiltrates the motor and increases resistance to its movement, causing it to be to slow in reacting to rpm changes. The rpm will rise and drop at an idle and in some cases it will go as far as allowing the engine to stall. If the IAC is stuck in the partially open position, the engine rpm will be high and will not return to an idle.

IAC Principles of Operation

Every movement of the accelerator pedal causes a coinciding movement of a throttle plate in the throttle body. The throttle plate regulates the amount of air to the intake manifold by its position. The more it rotates, the larger the opening in the throttle body. When the accelerator pedal is no longer being depressed, such as at an idle, the throttle plate completely covers the hole, eliminating all air flow into the engine. To compensate for this, the idle air control takes over. It is mounted over a hole in the throttle body just behind the throttle plate.

Under computer command, the IAC allows a regulated amount of air to enter behind the throttle plate through the hole in the throttle body. By regulating the amount of air, the computer effectively regulates the idle speed.

Remove and Replace the IAC

The IAC on the 2003 F-250 V-10 is a simple component to replace. Unplug the IAC wiring harness, then pull the throttle bypass hose -- the rubber hose connected to the rear of the IAC -- from the IAC. Remove the two bolts securing the IAC and pull the IAC off the throttle body. Remove the gasket from the throttle body, clean the gasket mating surface, and install the new IAC and gasket in reverse order of removal. Tighten the IAC mounting bolts to 89 inch-pounds, then tighten them an additional one-quarter turn.