I have a 2001 Ford Ranger XLT 4.0 SOHC and it still has a rough idle. Dropping down and picking back up for a few minutes and then picks up. Pulled the motor and replaced all timing chains and then replaced EGR Valve, EGR Solonoid, IAC valve, Mass Airflow sensor, DPFE Sensor and have check the wiring back to the PCM and it was all good. Im getting the code P1409 but I would've thought something I replaced above would have fixed it. Suggestions please