WHere to begin…lets see. 2003 Ford Explorer 4.6 liter AWD. Having some kind of VERY STUBBORN idle / emission problem. When it started it was an intermittent rough idle, mostly going too low or making a periodic “drumming” sound that could be felt and heard at the air cleaner box. CHeck engine codes were PO 442 evap system leak. I first cleaned and inspected throttle body, mass air flow sensor and idle air control valve. I inspected hoses for leaks, including spraying cleaner to see if I could detect idle changes / leaks. I then replaced Idle Air Control Valve. Did not seem to cure problem . SO took it into Ford Dealership and they smoke tested and said needed Vapor Management Valve and Vent Solenoid. I replaced VMV myself. Idle no longer “rattled” but when driving and braking the idle would drop down very low and sometimes not “kick up” and would die. I then took it back to dealership to have them replace the vent solenoid and reprogram the PCM. Still doing it. They said I might have a defective (new) Idle air control and to replace it- otherwise they dont have a clue. HELP.
Do you still have any codes? If so, then clarify / report and maybe I’ll change the below ->
Pull the vacuum line from your EGR valve. Plug it (a golf tee is generally the right size but anything will do). Cap the port on the EGR valve with a appropriately size vacuum cap - or similar. Maybe give the valve some moderate whacks with a rubber mallet or block of wood to make sure the valve is seated. Take a couple of trips like that and see what happens. This will set a code, and you can’t keep driving around this way. It’s just investigative
Or, if you can “catch” it while at rough idle, pull that line and see what happens.
If this helps then you first need to check the DPFE sensor first. But it probably means you need either a new vacuum solenoid or EGR valve or both. A vacuum gauge & pump will come in handy for figuring out which one. Don’t assume that this kind of EGR problem will set a code. I suppose it might sometimes - but not always. Ask me how I know…I needed the solenoid.
Get the evap problem fixed and verify the code doesn’t come back after several days of driving before assuming this problem is something else. Evap problems can confuse the ECM in setting the air/fuel mixture. Also, if fixing the evap problem doesn’t fix the rough idle, unmetered air getting into the engine is a common problem reported here, and can cause rough idle and surging, where the idle speed noticeably varies up and down for no apparent reason. Usually caused by a leak somewhere in the vacuum system. Split vacuum hose or leaky vacuum operated device, like the brake booster.