1996 Ford F-150 Idle High with OBD-II Code 1351 - ICM Circuit Fault
My 1996 Ford F-150 is experiencing a high idle issue and has been displaying OBD-II diagnostic code 1351, indicating an ICM (Ignition Control Module) circuit fault. I've already replaced several components including the throttle position sensor (TPS), idle air control valve (IACV), ignition coil, spark plugs, distributor cap, and rotor, as well as the intake manifold gasket and throttle body gasket. After clearing the code and running a lean condition test, the issue did not return. I replaced the ICM module, but was advised that it might be the wrong part or improperly installed. Despite these efforts, the high idle persists and the code 1351 remains intermittently present. Any insight into potential root causes or troubleshooting steps would be greatly appreciated.
A vacuum leak is a common cause of high idle in this vehicle. Have you checked the ICM linkage and flaps inside the intake ports? If they're carboned up or stuck, that could interfere with proper sensor readings and contribute to the circuit fault code.