Ford CODE 18: IDM circuit failure or SPOUT circuit grounded

The computer sends out a timing advance correction to the ICM over the SPOUT wire and then looks for the change on the IDM wire.

IDM - Ignition Diagnostic Monitor
SPOUT - Spark Output Signal from EEC/PCM
ICM - Ignition Control Module

You might check the ECT or the IAT sensor for your problem.
Also check the SPOUT/IDM wire going to ground.

ECT - Engine Coolant Temperature sensor and it has two wires on it.
IAT - Intake Air Temp

IDM (feedback) is a Dark Green with a Yellow stripe wire on the distributor connector.

IDM is pin 4 on the 60 pin ECM connector.

Ford trouble code 18