What Causes Idle Air Control Valves to Carbon Up?
- The only cause of carbon building up on the IAC valve is from the carbon that is in the fuel. Gasoline has carbon in the mixture and will run through the throttle and into the valve. The carbon begins to accumulate because the throttle does not burn off all the fuel in the component. The gasoline sits inside the throttle body, where the IAC motor and valve are located. The carbon sticks to the valve and slowly accumulates over time.
- The engine will develop specific symptoms when the valve has too much carbon on the assembly. The vehicle will stall, idle too high or too low and can misfire. The vehicle can also become hard to start or not start at all. Vacuum leaks or an improperly functioning IAC valve can both cause these signs.
- One way to test the IAC and determine whether it is the cause of the idle problems is to remove it from the engine. Inspect the IAC motor and valve to see if carbon is building up on the seating or pointed end. Keep the IAC attached to the power wires and turn the ignition key to the "on" position. The seating point will move in and out if the component is working properly. If you cannot hear the motor working, the entire IAC is bad. When you can hear the IAC motor attempting to work, but the seated point is not moving, then carbon is causing the valve to stick.
- You can prevent the carbon from affecting the IAC motor and valve by cleaning the component periodically. Just like changing your vehicle's fluids, you must also maintain the IAC motor and valve by cleaning it with a carburetor cleaner. After removing the IAC, thoroughly spray the component with the carburetor cleaner and wipe off with a clean rag. Test the IAC motor before placing it back into place just to make sure it is operating properly.