Legacy & Impreza Engines With No Injection Pulse #1 Cylinder

Built into the fuel injection control unit is logic that will shut off the # 1 injector if the computer believes that it can no longer control the Idle Air Control valve. Remember this while trying to diagnose a "hard" code for the Idle Air Control Valve or a dead miss in number one cylinder due to no injection at idle. A problem in the Idle Air Control valve circuit can be responsible. (Component testing shows that it most likely is not the valve itself.)

Another unusual computer response is if the computer is deprived of its "back up power supply". If deprived of this power, some computers will generate a false code for Idle Air Control valve and kill the injector for cylinder # 1. The pin location of this power supply can be found in the Control Unit Module I/O Signal pages of the appropriate Service Manual.